You dont think he is able? Men can have babys in there 80's. I would talk to him about it. Make sure he wants to have a kid trust me raising a kid by yourself is not the best way to do it. If he is not willing find another man that would be able to. If you talk about it with your boyfriend and it turns out you both want one. You ovulate 14 days after your started period.
My suggestion is not to get pregnant until your boyfriend is your husband, especially if he has two children. You don't want to be just another chapter in his life, you want to be it.