When I had an abortion a couple of months ago, the father was a guy I'd only been seeing for sex. He said he'd be supportive when I told him about the pregnancy, but the minute he knew the abortion was scheduled, he disappeared and I didn't hear from him until I was recovered and he wanted to get back to our old routine.
"Wanting to be a mother" does not mean you HAVE to be one. I still want children, in fact children are the only thing I absolutely want in my life, but I am still at university, I was not in a stable relationship and I was not financially able to care for the child - neither was the father, who is legally obliged to provide financial support for any child, whether or not he wants it. This guy you're with sounds like he'll say anything to make you feel better, but I very much doubt he means it.
Think carefully about it, but don't feel like this is your only chance for children. Don't let people make you feel guilty about your decision - it is YOUR BODY. Somebody said above that an abortion is with you for life - this is FALSE, a CHILD IS WITH YOU FOR LIFE, and abortion takes only a few days if you have one early enough. My abortion was only three months ago, and it feels like it never happened now.
You are still young, and being a parent is not something that stops when the child turns 18. Please please think carefully and do not get caught up in the romantic ideals of what having a baby is like. An abortion is just a short event, you can continue your life afterwards and it is not something dirty or shameful. Seek professional guidance, and do not rely on the man to stick to his word.