A lot of alcoholics get sad and maudlin and sentimental when they are drunk. Others get happy, angry, etc. You happen to have the sad/sentimental/maudlin type. The other kind is no easier to live with. Even the "happy" drunks neglect their families as they party on. The angry/abusive ones are probably the worst. But none of them is pleasant to be around.
If your boyfriend is newly sober, it takes time to develop what is essentially a new personality--one not fueled by alcohol. If he's working a recovery program that will eventually happen. You might or might not be compatible when the dust settles. But for right now, you just have to wait and see how things develop.
Are you doing something for your own recovery? I suggest Al-Anon--the more you focus on yourself the less you will be focusing on how he is acting.