The things that I've been involved with aren't things that are really "for" me anymore, I guess drifting away from leadership positions and a lot of the people kills the point of being involved, especially when you feel like a lot of your achievements have been forgotten or looked down upon. The organizations I've been involved with aren't ones that I will really be following up with after graduation so might as well prepare for that now. I think the same thing can be said for a lot of the people, as I will be moving across the country and only have so much capacity to keep in touch with people. It might be better than to start forgetting about them now than to have that lingering for however long into the future. This probably isn't the right way of looking at things, but it might be the right thing for me.
I feel you, been going through similar feelings with my girlfriend of 3 years. We talked - just aren't sure we are really 'for' each other anymore. We've pushed through difficulties in the past and gotten through tough times, but 3 years later and we just don't know if we should continue involvement with each other. Anyway... point is that it's quite hard to know when to walk away vs. when to stay. And I think the only way to know what to do in these situations is to accumulate experience, and it's kinda impossible to know what the right call is in the moment.