It's hard to be in a relationship in early sobriety because the more they love and support you the more you stand to lose if your drinking drives them away. If we can hold a job and manage our sobriety that is awesome. Sobriety, and a job, and a significant other? Now if we drink, we stand to lose so much more - make sense? So that added stress creates anxiety about relapsing, which ironically can cause us to convince ourselves to relapse!
He thinks you will leave him if he relapses, to make a long story short.