Why do guys leave and come back into your life all the time?

So i was seeing this guy for on and off for like over a year. We would be good for like a month and everything seemed fine then we would have a fight and wouldn't speak for like 3months and this happened 3times. The last time it happened we were getting really serious and then he decided he wanted to get back with his ex's. He didn't even tell me in person and he decided to tell me over a text that he couldn't date me anymore. Now after 2months of not talking he decided to text me telling me he misses me and wants to talk. I haven't answer him back and i dont know if i should and if i do wat should i say. Im kinda in the middle with this i don't know wat to do. I don't get way he keeps leaving and coming back into my life. I don't know if i can take anymore heartache with this guy he has already broken my heart a few times before. What should i do??