Yes, relapse is awful. All those old bad habits come flooding back for me. Getting stoned the moment I wake up, distracting myself all day with video games, reverting back to the habits of the depressive teenager I was, just now in my 30's. Every time it happens, I think to myself 'this is it, I can't come back from this one'. But I do.
The problem is, what am I coming back to? Starting again from square one, picking up the pieces once again, now a little bit (or a lot) older, with a little less hope than last time, and less of what precious little energy I had before.
Do you have access to any mental health professionals? It might be helpful to note the indications that you're heading towards relapse and getting some strategies in place to help cushion the fall. I recently relapsed, but I had a few things in place so I didn't crash as hard. But still, hard to get back up again when there's nothing to go back to.