My boyfriend doesn't seem interested in hanging out with my family. How can I bring this up with him?

[Leah M]

My boyfriend and I have been dating for about 9 months now. I've met is entire family, and spent time with them. He is eager to invite me out with his friends and family dinners/events. I always try to go, and I LOVE his family and the friends he has!

But whenever events come up with my family or my friends and I invite him or ask him to go, he always says 'maybe' leaves it as that, or he says 'he's got something else to do'.

At one point, there were a couple of events (one of them being one of my good friends weddings) where I asked him about going, he said he 'might of had something to do', and I went to her wedding, alone, and he was upset because he said I didn't invite him.

This has become a pattern, and I really care for him, and I've always thought that this is someone that I could be with long-term. But this is the only thing that frustrates me about him.

How can I bring this up with him, without sounding too selfish, or too frustrated?
He's only met my parents like twice, and I've met his mom, and siblings quite a few times and spent time with them!