My boyfriend is nuts i have tried?

i know the answer to this but i feel as though i am going nuts myself. So much has happened, and i have really tried, this is my first relationship and i have been through 2 years of hell, but this glimmer of this guy being able to treat me right is what keeps me......lately though, i added a random artist on fbook, he added me, and i declined, he then messaged me saying he was an artist and was adding me coz he was a friend of a friend, i messaged back and said cool and sorry i don't usually add randomers but i was too quick to judge, so i accepted his add, he msgd back saying thanks and he can see why i declined in the first place....my boyfriend sat next to me and was on my laptop and went through my messages, when he saw this and i said i done nothing wrong wtf he went nuts, and ran to the kitchen to get a knife and was trying to slit his throat, eventually he left my house and i went in pursue as didn't want him to do nething stupid, i told him to get in my car and proceeded to drive him to his mates house where he could cool off, he also threatened to jump off a balacony, im stuck....he has worn me down so i have no self esteem, but part of me wants to be with him.....i know its stupid and please don't say so but what do i do?