Hormones or incompatibility?

My SO and I have been dating for about a year and we just found out that we are expecting twins around February!! But...he and I have a somewhat toxic relationship. Let me explain...he is a retired army veteran and as such certain issues (PTSD, Anxiety, Mood Swings, etc.) were expected. He's come quite a long way in his battle against these issues but still has hiccups. Major ones like he sometimes loses it and hits me....granted less than 30 seconds later he is apologizing profusely and crying while begging for me to forgive him. I just....I don't know what to do. I love him with every fiber of my being and I can't imagine living without him.....I just get scared sometimes. What should I do?