For better or for worse question?

I am in a relationship with this guy...and he has been sick the past few months. Well things are finally on the mend but Throughout all this he has snapped at me and been really depressed and I would too if I had been dealing with this for a long time. But my thought is, if he is this way now is this a preview of how he will be in the future? Just a little side note. I started dating him about the same time he got sick, so I don't know any other side of him. I'm a nurse, so I can handle most things including sickness, but I'm just weary of someone thats a grouch all the time.