Help!

So my fiance and I have been together for over 3 years and he has a 5 year old from a previous marriage. However we can't have sex. At first he said he had a tight foreskin and I was too tight and very recently he said it happened when he was trying with his ex wife to conceive his son. He said the pressure was too much. We have had sex on four separate occasions but only when he takes Viagra but he says the Viagra makes him feel ill. I've cried and asked him to be more affectionate and for us to work on it. I've tried sexy lingerie and toys but my confidence is so low I can't even initiate it anymore. I love him so much but I can't talk about it anymore as he says I'm pressuring him. Has anyone got any ideas or tips?