I don't think he wants to exclude me in their dinners but godparents never asked or invited me over and because these dinners are hosted by godparents at their place, BF can't really invite me without their permission.
Hmm. Could he say something to them like, "Godparents, I've been dating
Josieh for (however long) now, and it would mean a lot to me to introduce her to you and have you all get to know each other better. Could I bring her to dinner this Friday?"
Because there are etiquette rules about not inviting only one member of an established couple, I think it would be OK for him to politely ask to bring you like that. But they probably won't invite you if he never says anything to them about it.
How they react will help you figure out how to proceed. If they say "Oh, we didn't know you were dating
someone seriously, we'd love to meet her! Of course bring her to dinner!", the way true godparents should, then that's great.
If they get upset and seem to think that it's inappropriate for him to bring you, or for him to be dating
someone seriously, then that might tell you that there really is something wrong here (such as maybe they're still trying to keep him as a widower-son-in-law).
My concern is, certain people think more than that and expect something more out of the relationship. I can see that BF don't care for the dinners or the get togethers but knowing that they're going on a trip together makes me nervous about the whole situation all over again.... I would also be flattered if godparents invited me on this trip but I think this is all BF's wishful thinking....
It sounds like BF is conflicted or uncomfortable with things the way they are, but is afraid or doesn't know how to try to change things. However, if there's something wrong in the situation, if these people aren't really going to be true godparents in the long run, but are just trying to hold on to the past, then it's really important to find out sooner rather than later, especially if he risks losing you over this.
Your BF can be respectful of the godparents, and sympathetic to their emotions, without necessarily going along with everything they ask for. He has every right to ask for you to be invited to dinner along with him, or to start spending less time with them if they refuse to accept you.
If it's not even clear whether the godparents have actually invited you on the trip, or if BF was just planning on sort of springing you on them, then I -really- recommend trying to test the waters by trying to be included on the dinner first. That should tell you both quite a lot about the true situation, and where to go from there.
And, of course, if your BF ends up being too conflicted, or too unwilling to rock the boat in order to make sure that you're treated as his girlfriend, then that tells you something important as well.