I posted a reply but it didn't seem to show up? So I'm trying again.

They broke up because basically she wanted to travel and try new things, and he didn't want to go with her so she saw that as not being committed to her. She said he was immature and wasn't ready to move out of his parents place and do more with her. He now says that he's changed and is trying to convince her that he'll do more of what she wants.

And, with the wedding invite situation, we've only lived together 3 months and the invites went out mid-last year. I think RSVPs were due around last June before we even got together. They planned this wedding very early. We did discuss later in the year about trying to get the couple to add a +1 but at the time I didn't see it as a big deal, I just thought it would be fine to skip it since it might be a hassle to shuffle things around. If I had known this ex-BF thing was going to pop up and be super annoying then I would've pushed for it.