you say you're afraid he'll choose to be with you anyway and that you don't want him to give up having kids for you. Isn't that his choice? If he gives that up to be with you that's up to him but at least the separation isn't under false pretenses and if he stays he has the reality of what is before him rather than either breakign up with him without telling him the truth as to why or letting him stay and pretending it might change. Being honest in a relationship is job #1 period.

Also you should stay because you're happy with him and choose to remain for reasons other than those things, in a good relationship any challenge can be overcome but the most important part is that the two people are there because they want to be. It doesn't make sense that if you love him and want to be with him that you would choose to leave based on assumptions of a future that may or may not come - that is children and your sex life coming back or not, etc.

If you want to stay in the relationship, be up front, honest and tell him right away about your feelings because it doesn't sound like your fears are based on lack of love for the guy but fears alone. He deserves to know and deserves to make the choice to stay or to go based on the truth and not have a break up forced on him by someone that loves him but is protecting him from making the "wrong choice".