Meeting the ex's friends for the first time since breakup

[Dunderman]

In January, a three-year relationship ended for me. We stayed friends through the breakup and today she is my closest friend.

Her birthday is coming up, and just now she invited me to a restaurant this weekend with her family and a bunch of other friends. During our relationship, I got along really well with her friends, which is unusual for me. I hoped I'd stay in touch with them, but it just didn't work out that way, so this is the first time I'll see them since a couple of weeks before the breakup. And I don't know what to expect, nor how to act.

There's in particular this one girl, with whom I was quite close. We hugged when we met and had tremendous fun together. Then I didn't see her for a year. I have no clue how to relate to her.

Any advice? Any thoughts?