Oh gosh that is a difficult situation, I can understand why you are going around in circles.

It seem like to have some one who is a 'maybe partner in the future' fathering a child would put a huge pressure on the relationship and might kill it before it even gets a chance to find it's own feet. I just think it would be hard to build a relationship with him in such an extreme situation IYKWIM. And what it he turns out to be not such a nice guy, where would that leave you and your second child?

Would you be able to use the services of a sperm bank to allow you to have child number 2, then you can see how things pan out with the nice guy (or another nice guy should one happen to come along) without the pressure of him being the father and having to have a role in there somewhere. Sorry I don't know if this is an option for you or not.