How can you tell when irritability and agitation turn into emotional abuse?

I've been dating my boyfriend for a little over seven months now. As of late his workload has become more strenuous at school and he's become more and more easy to irritate lately. I normally end up in tears or alone because he's gotten so angry at me it's made me try to get away from his as fast as I can. How can I tell if this is just stress, or if he's become addicted to venting his frustration out on me, or in other words, emotional abuse?