I want another baby!?

ok long story i was with my boyfriend and we split up when i was 4 months pregnant and he got with another girl and they have a baby and they split up and he got a vasectomy (had two kid and paying child support for both did not want to have to do it for another). well it has been 3 year since we split and then about 7 months ago we started talking as friends and about 5 months ago we started dating again and we are living together. but i am 21 and have one son and i now that i want to have another baby and i don't know what to do he kind of knows that i do and he says he is scared that it will get to a point to where me wanting a baby will drive us apart. i know that he can get it reversed but it will coast $ 3500 but to do that and then have a baby then to not want another so i don't know if it is worth it and he has never said that he wants to do it and i just don't know. if any one can help please do i am stuck.