An addict cannot use "once in awhile" or just once to "get it out of my system." Period. I've been in that same place, where I was told "I just needed to do it one more time", been hopeful, and then devastated when it quickly spiralled into full blown active addiction. Fortunately he quickly realized how out of control he was and sought help. He too had been clean for about a year before he relapsed.
As for how to deal with any resentment... you have to constantly remind yourself that it has nothing to do with you, even if he tries to make it about you. I am learning this lesson very slowly. And it takes effort and time. If you read enough posts here you'll quickly come to understand that you can't change the way he feels, all you can do is change how *you* feel. Work on reclaiming your own identity and your own life. I think that most of us who have lived with and loved addicts have trouble with that, but to begin that work is one of the most empowering things you can do for yourself.
My AH has very moody/angry days. My plan is, if his negativity is ever really getting to me on any particular day, I'll just look up times for an Al Anon/Nar Anon meeting and attend one. Work/school/dance has kept me from going as regularly as I would like, but knowing that that support network exists helps a lot.