I am sorry that you are hurting, Sidony. I have been in your shoes, as I remained friends with my frist husband for 12 years after the divorce, often being in large and small groups with his new gfs and wife. It too me nearly 20 years to realize how much I was hurting inside by doing this.

I respectfully offer a different view from Pat's. I and I alone am responsible for my feelings.

Your X has moved on in some important way. You haven't. That's not his problem. If you can't enjoy being in a small group with him, don't go, and start making new friends.

I'm sorry if that seems harsh, but I have found that the cleanest choice I can make is to not hold other people responsible for my feelings. In my case, I denied the inner hurt, because my X was my best friend and an extremely intelligent, entertaining, and resourceful man in the same occupation as I was. Denial was not a healthy way to "take responsibility" for my feelings.

Making myself responsible for my feelings has made it easier for me to establish boundaries and to decide how to respond to boundary violations.

If your boundary is that you cannot be comfortable in a small group with your X and his new gf, you must tell the friend who extended the invitation about this. You must ask if your X will be there with his new gf every time someone from this group extended an invitation so that you will know what to expect. This requires you to reveal your vulnerability, but that is a human quality -- a human quality that I denied in myself for far too long.

Once these friends understand that they cannot have both you and your X, the decision is the friend's about whom to invite.

If you are not invited, that will hurt, too. But again, the friend extending the invitation is not responsible for your feelings either.

Unfortunately, after a break-up, friends tend to get divided into HIS and HERS piles, like everything else. I respectfully submit, on the basis of my own experience, that wanting to hang onto the old circle of friends lead me to make a poor choice about denying how much it hurt. The pain is real, and it's okay to feel it.