Boyfriend change his mind...

so we go engaged on xmas and he was totally with it, until I got pregnant and now he acts so distant and he says he loves me but doesn't want to get married anymore... I'm 19 and he's 25. we have been together for awhile, we've been living together for a year now. I don't know why he's acting this way he can never tell me. He said he was having doubts but he said he's always Yas doubts about every relationship he's in. I wanna get married before the baby's is born I always wanted to have a kid in marriage. (just what I always wanted) and since we were planning todo a month before the due date it worked out and now it'll never happen..... Im so depressed now.