the life and recovery of an addict has its ebbs and flows. i think it is significant and encouraging that he had two years clean before relapse. relapse is a common occurrence in addiction, and some addicts have to relapse a few times before the recovery really sticks. it always concerns me when partners of addicts end the relationship altogether rather than separating while the addict takes care of business, if the relationship and the recovery are both young. things are not black and white, cut and dry, with an addict, and being able to move with the flow is a necessary part of the relationship, in my opinion, if one is taking the long view. but you have to have the commitment and the desire.
all i can add is that if he returns to recovery sometime in the coming months, and asks you to wait for him to get back on track (maybe a year) and you want to, then do it.
while you are moving through all the pain right now, read all you can about addiction. i believe our thoughts and hearts connect to our addicts through time and space, and the more you are grounded and informed, the better for you both.
the time you had together, clean and sober, was beautiful and my hope is that after some time of misery and terrible isolation, he will do what he has to do. you'll have to wait and see.
all the best. it takes time. lots of it.