Why he do this?! again?!?

Ok so me and my bf have been together for a year and a half and we've had several break ups in the relationship. First was in this past october right before homecoming. Than the second one right before prom last may. NOW he broke up with me again two days before my open house?! And all these break ups r random no fighting leading up to them one day we're hanging out everything is fine the next day "BAM" he is pissed and never wants to talk to me again and than he comes back every time. But i mean two days before my open house?! there are pictures of us ect. I mean everyone expects him to be there....Why does he keep breaking up with me before big events but get back together with me right as soon as their about to begin?! this is the third time idk if he's coming back and if i care anymore.