So, I've (28F) been with my boyfriend (29M) for about ten years. Early in our relationship we were both diagnosed. I have a personality disorder and he is dealing with psychosis. Our disorders have been up and down through all of this time, but the last few years have been rough for us both. I believe he is hurting more than me, though I go through periods of depression and suicidal thoughts. Lately I've been focusing more on my needs, of what I can do to feel better. I try my best to be mellow and chill to keep the destructive thoughts away. To do this I need peace, quiet, structure and predictability around me. Unfortunately, my boyfriend is emotional (I'm not really) and can go from happy to sad or angry in 0.1 seconds because of his mental illness. And this affects me. Not that he is ever violent or yells at me, it's more focused inward on himself. I go from feeling mellow to sad and annoyed. Like I absorb some of his emotions. 
I never know when this will happen, and it is starting to make me feel like I would be happier on my own where I can control my surroundings better, and make sure there isn't this "sudden negativity" floating around.
But I feel so guilty thinking this. It's not his fault he is this way, or that he gets sick. But it affects me, and I feel like I run out of empathy. Whenever it happens I just think "if I was alone, I wouldn't be annoyed right now, I would still feel calm". 

Am I too selfish for thinking more about my mental health than his (arguably) worse state?