What is wrong with my partner?

Hey all im needing some advice, my partner and i have been together for about 18 months, everything was going great (if a little fast) and last November we were going to move in together. 2 days b4 we were ready to move he broke up with me, we got back together a few days later and i just put it down to him having cold feet. Everything was good again until February this year, when on a night out he broke up with me again, he said some really horrible things to me and also told me that the reason he broke up with me in the November is because he had a one night stand with another girl, although they didn't actually have . Anyway 6 weeks later we got back together AGAIN. About 3 months ago he asked if he could move in with me, i said yes aslong as he wasn't going to change his mind at the last minute as it wasn't fair to me or my 8 yr old child (not his child) Anyway things have been fab between us, until yesterday when he started being really quiet and subdued again, i told him last nite i didn't like it when he was like this as i get paranoid as its the way he was acting before the 2 times that he broke up with me. He didn't answer me!!! I know he has alot on his mind just now, he is a construction worker and in the current climate he is not always guaranteed work and to make things worse his car broke down yesterday and would cost more to fix than its actually worth!!! So i know he s mega stressing about money especially with bloody Xmas just around the corner, but im worried he is going to do what he did last Nov an in Feb this year :( What do u think? And what can i do?