Limp dick

So I have a boyfriend that's 22 and I've known him for a few years but we just recently started dating. Anyways he can get hard but after he puts it in he goes soft. I've NEVER had this kind of problem before and I have no idea how to handle it. I already have a 1 year old but some day I want another baby, but I'm worried if I stay with him I'll never be able to have one