I'd only have a kid with the person I'm married to.
Why is that a problem?
I don't think anyone would want to get married to me, but I really want to have a kid.
I imagine that must be a difficult situation. But if that's who you are, that's who you are. Other people are in the same situation and find a way to make it work.
You say that, but you don't know how hard it is.
I can understand how you feel, but you shouldn't give up hope. I'm sure you'll find someone you love and want to marry, and then have a child with them. There's nothing wrong with waiting to find the person that's right for you.