My fiancé can't cum ! Help !

Ever since me and my fiancé have been together, he has always had a hard time cuming during sex. We have a 1 year old now and the only reason I got pregnant was because he used viagara at the time. It's been about 3 months since i have been able to make him cum and during sex he will go soft and it will be over. The only way he can finish is if I give him a bj or hand job. He had a very extreme health problem when he was young that affected his nerves. He says that sex doesn't feel amazing for him and it has been like that from the first time he ever done it. He also says he can't stop thinking during sex about trying to cum and it makes him go down. He doesn't want to keep buying viagara so I don't know what else to do. I feel really insecure and less like a woman. Is anyone else experiencing the same thing and know what to do ?