Totally normal to be triggered by what may be construed as a replay activity. I get it. But I think it is very positive that H wants to discuss it in therapy. I for one, always took girls trips. I stink girls/guys trips are actually quite healthy. However, in this scenario I can see how you would feel left out again. But maybe there is an opportunity to also celebrate his 50th as a couple in addition to this guys trip.
Anyway, what I see as important here is that you communicate how this makes you feel and why. I am sure there is still some amount of self-centeredness in his not-quite-fully-cooked MLCer brain and likely has no idea that this could possibly impact you at all.
Remember, it takes time to re-build what has been completely destroyed. Time, patience and baby steps.
Hugs friend.