I think that you’ve gotten to the heart of what you are facing.
I would summarize the issues as:
1. Commitment: “If he cared he would…”
You have believed because of the warmth of your relationship that he Should be committed in particular ways. He Should focus upon you and your emotional and sexual needs instead of not hearing you and being self-centered. You have believed that if he was committed to you, he would buy viagra or let you buy it for him.
You want sex – that includes intercourse that lasts more than several minutes with him losing his erections. You want sex – where your feelings and needs are a part of it.
You are very hurt that he’s apparently tried to have sex (and probably failed related to intercourse) with another woman while you were supposed to be out-of-town.