It seems to me that your boyfriend isnt being respectful of you at all. Come to that, you arent being very respectful of yourself.
He drinks, gets horny and then cant perform. At this point he blames it squarely on you.
When you accept the blame and try to make it better, it allows him to keep behaving this way.
Let him know that it isnt ok with you, if youre good friends, he will try to see it from your point of view.
In the meantime, you are not responsible for his behaviour and you dont seem to have done anything wrong.