I'm afraid my SO will leave if I can't have a baby..

I have a son from a previous relationship but my SO doesn't have any children. He cares for my son but wants his own too and I want to have a baby with him. We have been trying a while now with no luck. I am worried he will want to leave if I can't have another baby. Anyone else feel the same? I know he loves me but I know he really do want a baby as well.