he thinks I don't want a kid with HIM??

So my woman instincts are giving me huge baby fever. I've brought it up to my SO a lot but he's not on board, which is fine. But today he said "we can have a kid when you want one with me, not just when you want one." My heart is crushed... I'm so in love with him. Head over heels. I've even considered proposing to him. I had no idea he felt that way? How do I prove to him that I want a future with him and I want to have HIS kids and not just anybody's...