When I first got sober this time around, my biggest fear was relapse, I didn't think I could do it anymore. I listened to lots of audio on relapse and peoples stories about relapsing, sadly your sponsor has probably taught you so much by you witnessing what he is going through. Hopefully he gets back to the program. if you told him what you posted about how much resentment he is holding in and suggest that may have led to his relapse, hopefully will listen with an open heart.
CaiHong