Get Help or ELse

My boyfriend keeps giving me this ultimatum. Get help or I'm leaving. I can't decide it it's a threat or some sick and twisted way of motivating me. So I tell him to leave. Regardless of the fact that he's the best thing to ever happen to me and I'd probably give up on life all together without his support, I still feel like anyone who can threaten to leave me when I need them the most might as well just leave. Does that make me selfish? To ask him to stay and endure this battle with me though I know better than most how demanding, challenging, and merely impossible this road can be? But isn't this what he signed up for when he promised me forever and took me to that first doctor's appointment? Or am I asking way too much of any man, for he's only human. No one wants to deal with this...the ups and downs, the crying, the fits of rage, the physical harm, the emotional, physical, and mental stress. No one wants to deal with that. Not parents, not teachers, not friends, not doctor's, not significant others...shit, I don't even want to deal with it. So who am I to stop someone who has the will power, strength, dignity, future, and most importantly the RIGHT to walk away from this mess? Who am I?