Advise and help on my relationship please!!

Ok, so I'm totally in bits and I have no idea what to do! Me and my boyfriend have been on and off for 2 years now, we have just got back together after being separated for 3 months, in which we both saw other people. I'm starting to realise that this time I've become very obsessive and always want to be with him. I've also noticed that he doesn't seem to be putting in as much as an effort as me. I addressed this with him, and he told me that he doesn't want to get "too attached " becashe he doesn't think it is going to last, due to the previous times we have been together. This obviously really upset me, seen as though I haven't even thought anything like this. I thought this time was going to be different, I thought this becashe thoughout our relationship one of us has always had more power than the other, it's always been me, expect for this time. This time he's got the power and he's totally taking advantage of it. He's ignoring me on text, taking forever to reply, and it's really really getting me down, I just need some advice of what to do.