Jan needs to grow up.
That is one thing I think every Doper in the world would agree on. 
Totally unweird.
Divorce doesn’t have to split every relationship up and force everyone to choose sides. I’m reminded of this at every holiday get together with my in-laws. My MIL has been divorced for over 30 yrs. Her ex-husband’s brother’s ex-wife (so twice divorced from MIL, relationship-wise) is still a regular at Christmas time, as is MIL’s ex-mother-in-law. What’s funnier is MIL’s ex-husband’s brother still attends also, and brings with him his long term significant other. No one seems to think this odd at all. They’re just one big happy family.
People form families and relationships any way they chose to. They’re not required to break them off at someone else’s behest.
And another vote for not weird.
My ex is still good friends with my father, and I have always liked my ex’s mom a lot. That may have something to do with my ex having lost his father, and me missing an grandmother.
My ex and I both go out of our way to encourage contact. I will encourage my dad to call my ex to go have a drink, and when he is with his mom he finds some excuse to let her call me. “Oh, I’ll put my mom on the phone. She wants to hear all about the new kitty. Here she is !”.
Count me in the “not strange at all” group. My father split up with his ex-wife before I was born, however the divorce was amicable and they still talk every week. When I went to California, I lived in her house for 6 months. I nearly went to school at Berkeley and she and I discussed me establishing residence in her house. I talk to her every few weeks and I have never found it to be particularly strange. Granted, she is the mother of 4 of my siblings but other than that there is no reason for us to be so friendly.
My mom’s aunt Nancy died a year ago. That doesn’t make Great-Uncle Don any less my great-uncle as far as I’m concerned. I like him a lot better than some of my blood relatives! Until we moved a state away, I was close to my mom’s aunt by marriage too. Even though I barely ever spoke to her husband, who is the one I’m actually related to.
My husbands brother and his wife divorced after 20+ years of marriage. We got custody of the sister in law and maintain a close, loving relationship. She spends every holiday with our family.
Some family you’re stuck with through birth. Some, you’re lucky enough to chose 
(then again, in our immediate family very few are related biologically, so we’re probably not a very good sample group)
It sounds like Jan is bitter about the cheating and would like for Bill to be ostracized as “punishment” for that. I really can’t blame her for that. I can totally understand being angry enough abotu cheating that you want to remove every trace of the person’s influence on your life. However, just because he was a lousy husband doesn’t suddenly mean he’s a lousy uncle too. I definitely understand how the niece doesn’t want to be put in the middle of their divorce, and wants to hold onto a relative that she has known since childhood. As long as it doesn’t seem like anything sinister is going on as far as Bill trying to get a romance started with the girl (which would definitely seem gross and disturbing), I think their interactions are harmless.
Another vote for not weird. My mother and my stepfather got together for years with my father’s nieces and nephews (my cousins on my father’s side of the family). I ended up with four parents (my father remarried as well).
Nope, not weird, and not nice for anyone to try to pull them apart. As Anaamika has already brought up, she is an adult, she can make her own decisions.
My uncle dated an awesome lady for many years, and her and I grew close. They had a very messy breakup, and he would come over to my home all the time and beg, plead, and sometimes DEMAND I not speak to her, not talk to her, not associate with her. His reasoning? “She’s the devil! And she’s from HELL!”
He died over a year ago now, and though I miss him desperately and will always love him… *the devil * and I are still good friends.
Why are the ads about dating sites?
My memories of my aunt’s first husband are very vague; it’s been close to 30 years since the last time I saw him. His choice… he’s gone so far as to deny to my cousin, upon a chance encounter (they live about 600yd away) that he’s ever had a daughter. But I called him “uncle” for 10 years and still think of him as “uncle”. My uncle who’s a turd, but hey, some of the bio ones aren’t particularly nice either.
Aunt’s second-wedding 20th anniversary is next month. I need to think back to how old my cousins were when she left them in my grandparents’ tender care to marry second-husband, who’s always made it very clear he doesn’t consider himself related to us, or even to her children. Only one of his sisters has had any interest in being a relative to my cousins (he’s got five sisters and a brother). 20 years and I don’t think of him as “uncle”, but like I said, he’s always refused the name.
After running into his (separated) wife when he went to meet The Nephew, one of Dad’s brothers asked the Proud Daddy “you told The Idiot?” “Well, just because she’s the one who started the paperwork, doesn’t mean she’s stopped being my Godmother!”
The rest of the family has either sided with him or simply continued ignoring both except for chance encounters, like they always had. One day he’d been ranting about The Idiot and the evil of females in general, his sister got fed up and told him “maybe it takes an idiot to put up with you for forty-five years, you know.”
Quick back story:
My SIL (my ex-husband’s sis) hated my guts with a vengeance and many years ago we ceased contact. Even the death of my ex was not enough to bring her out of the woodwork for the funeral.
However, since her two boys reached the age when they could think for themselves, they have maintained a close relationship with myself and my kids (their cousins). One of them lived with me for a few months, and the OTHER I only just managed to kick out of my home (after 4 years) and now lives in the next street, visiting every second night (for a feed mostly!!).
In other words, not weird. Even less so since the SIL herself passed-away last year, leaving the boys motherless and their dad in another state (geographically and emotionally).
Unless the guy is some kind of weirdo, no, I don’t see anything wrong. My wife and I are married 20 years, together 24 years. I have known her sister’s children that long, most of their lives–her youngest, for her entire life. They all took vacations with my wife and me at various times, we get together every Christmas and birthdays and such. I love them all, my sister-in-law included. And I love the kids (all adults now) not in anyway different than I love my brothers’ children.
My wonderful wife and I are in no danger of divorce. But hypothetically if we did, I’d be hurt if her sister’s kids didn’t still love their Uncle Bob and stay in contact. I would not think of myself as an “ex-uncle.”
My biological uncle John and his wife Patricia divorced - shit, gotta be 22, 23 years ago. Later on we were going to the marriage of their daughter, my cousin Diane. I said something to the effect of “It’ll be cool to see Aunt… uh, I guess just Patty…”
My father whirled on me. “She’s still your Aunt Patty, and don’t you ever forget that.”
And so she is. Wise words, IMHO.
Not at all weird.
My entire family is still good friends with my Uncle’s second (or possibly third - I loose track with him) ex-wife. In a good many ways, we’re closer to her than to him.
In fact, my Aunt (the Uncle’s sister) gets together with that ex three or four times a year to go to the symphony and have a nice dinner out. She is invited to all family functions. She often chooses not to come (because if my uncle is going to be there (which is by no means a sure thing) it’s a wee bit awkward), but she’s always sincerely invited.
Unless there’s some non-divorce-related extenuating circumstance, there is no reason at all for an adult child to cut off a former spouse.
Similar situation for me. My mom’s sister divorced her husband 20 years ago. About 10 yrs ago my cousin was getting married and we were gathering outside the church. I was standing with my mom and her other sister and I said, “Oh, look! There’s Uncle Glenn.” My aunt (not his ex) said, “He’s not your uncle any more.” I just glared at her and ran up and gave him a big hug and said, “Hi, Uncle Glenn” and he was just so pleased that I still considered him my uncle even though I hadn’t seen him in 10 yrs. He’d been my uncle for most of my life and had taught me to ride and care for horses and stuff like that. How could he not still be my uncle?