Ok im a lil different to most. If you have no support/family etc, it can be hard to let go of an ex's family. I think you need to have a convo with your ex and be honest about your feelings. Your feelings about him but that u get it's over and about his family. If he has a new gf and u r truly supportive, great! When his family invites you, try saying "oh are "ex bf name" and "new gf name" coming? It would be great to see them!" That's the best sort of support. Do u get along with his new gf?

Lastly maybe think why u r friends still. Do u wanna stay friends with the hope of reuniting in time? Or just because u enjoy the friendship? If it's just for the friendship, u need to champion his cause and his choices.... particularly with his family.

Good luck!