I hear the love between the two of you and how much you care and want the next level of closeness. You are correct that the Bar Mitzvah is a huge milestone and while I can understand your desire to be there I can also understand why it may be the better idea for you not to be there since you are not in that level of relationship at this point. Dinners, intimacy and his desire is there but this next level isn't there currently. It is your choice whether to hang with him and be intimate in the hope that he comes back around and wants more and if you feel you can't then you get to decide what works for you, but try not to let the bar mitzvah be a sticking point for you.
I await your thoughts.