Lucy,
I'd say that you could be correct, as I have experienced similar situations, except from the guy's perspective. If it's any resolution to you, then what your boyfriend may be going through is his own abandonment need, perhaps brought on by something similar than what you or the rest of us had dealt with growing up under alcoholic parent(s).
If he's withdrawing, it's not a great sign, but it's not your fault either. I wish you luck with this, and I hope it turns out to be just something minor and that you will both continue on, happy as can be.