My parents divorced when I was 10. They’ve both remarried.
My mom remarried to C when I was 14. I like him, but it’s more a sort of “he’s a pleasant guy to be around.” He’s not a replacement dad for me (but is for my sister, who’s 5 years younger than I am). He never tried to parent me - that was always my mom’s job. He’s a quiet, occasionally silly guy. Not extrovertred, kind of naive, sweet. Because he never tried to parent me, I never resented him for “trying to take my dad’s place.” I get the feeling that he’ doesn’t think of me as his child, but he still respects me and will help when I ask (“Hey C, can you help me build this?”). I’m okay with that, because that’s how I feel toward him. We understand each other’s boundaries, and respect them. I don’t have any bad stories of him, but do have one or two pleasant ones (My mom tossing at oven mitt at him from across the kitchen, his tasty steaks from the grill, the time he drew an eye on a water bottle lid and held it over an eye with his face muscles).
My dad remarried in 1999 or 2000, to K. I don’t like her. She’s extroverted, likes to play pranks, tells dirty jokes, and tried to parent me. I’ve only met one of her children (my step-sis), and I don’t want to be like her. She’s the kind of girl who takes after her mom by being the type to scream at someone when she gets angry. I get the feling that I’m her husband’s daughter, and that’s it. She’s not helpful, she doesn’t respect me. When someone doesn’t like you, you can tell.
I got food poisoning when I lived with my dad and K for a short while. I was absolutely miserable and thought I was going to die (well, at the time, you know how it is). I hadn’t puked in a decade, so I didn’t know where the Pepto was. Cody woke her up to ask (she works 3rd shift as a nurse, and my dad was at work). She bitched him out for waking her up. After that, he had to rummage through the house to find clean blankets, since I’d puked all over mine. Cody went to the store to get a specific kind of soup (Healthy Choice Chicken Noodle), since it was all I thought I could stomach. When I finally feel well enough to walk, about 12 hours later, I go to the kitchen to eat my soup, K (who does all the grocery shopping and thus should know that she buys store-brand soup and NOT HC) had eaten my soup for supper. When I asked her why, she yelled at me for “not labelling my can.” It had been in the cabinet for about 3 hours. I started just sobbing, then got dressed to go to the store to get more soup. I’d been puking for about 10 hours, on and off, falling asleep only to wake up 10 minutes later to puke. I was exhausted, dehydrated, and starving. She doesn’t offer to make me anything else. I had to drive 20 minutes to the store in this state. All I got before I left was, “are you good to drive?” from my dad. “No.”
So, I guess what I’m trying to say, is that if you don’t like the kid, I’m SURE he can tell. I could, and still can. He sounds a lot like me (well, except that I’m 20 and don’t make my mom cry), and extroverts and introverts don’t always get along. He might resent how well you and his siter get along, like you “picked” her. Doesn’t make sense, but when I was 16, I felt like anyone who was athletic and out-going would always be favored, and I never would be because I wasn’t like that. Seeing his step-dad take an interest in his athletic sister might “prove” that to him.
How’d the custody thing happen? Cause there’s that idea that “preppy” folks are favored in your part of the family, while geeks are merely tolerated. There’s a lot of insecurity at 16, and if he spends all day at school being “not as good” as the preps, then to go to his mom’s and feel the same way, that can be shitty.
Or he might not want to go over there because it’s boring. How far away is it? If he’d rather spend weekends with his friends gaming, but is being “forced” to visit his mom, that could make him resentful. I know he doesn’t have chores at his dad’s, but does he have a lot at his mom’s? He could feel like he’s being used as a workhorse. “Great, you’re over for the weekend. While you’re here, mow the lawn, do the dishes, and clean the bathroom.”
Whatever the excuse, I do think that your mom and him (and quite possibly the father, too) should have a few sessions of counseling. Or maybe the son by himself. But don’t be like, “Why are you making your mother cry? We need to figure out what’s wrong, so we’re going to counselling.” More like, “We know this is hard on you, and we think we should all go to counseling and work out this new situation together.”
I’m just tossing out ideas, since I was a teen not so long ago, and have two step-parents.
Maybe he’s just an ass. I don’t really have enough info to know what’s going on.