My fiance and I have a lot of the same friends, so it's hard to say how I'd feel about it, but I doubt I'd be worried or anything. We have a good life, we're happy, we talk so we know we're happy and not just assuming each other is fulfilled in the relationship. He has some happy hour things with his work, but I don't go. I'd be bored silly. lol I go to lunch with he and a co-worker sometimes, but only because we have stuff in common and it isn't forced.
If you're worried about that situation, talk to your significant other about it. They may be able to stop your fears or validate them. But if you're concerned because of something an ex did, you're no longer dating your ex so don't put that fear on your current partner.