The bloke went out with a mate. He texted twice during the evening. Exactly what 'thoughtless mistake' did he make?
I wonder what you response would be if the OP was a man.
He has done something which according to the OP is out of character that has hurt her. If he is a kind person, who doesn't want to hurt his girlfriend, but it happened because he was visited unexpectedly by a friend, started drinking and then went out because he wasn't used to it, I would classify that as a mistake.
Clearly that is a purely fictional conjecture, but my point was, he has hurt his girlfriend. He might have done that by mistake, or he might be someone who doesn't care as much as she thinks he does.
I am not trying to judge whether his actions were normal or not. Obviously, in most relationships, his actions would be completely normal. But each relationship has its own 'normal' which depends upon the two people involved. From what the OP says, his actions here are not part of their normal.
I answered as I did because I think the OP might be in danger of over-reacting, and thus push him in exactly the direction she doesn't want him to go.
She mentions there have been problems lately. This needs to be addressed calmly. If he is feeling oppressed, then it is better that is discussed than that she pressures more and he begins to behave in ways that hurt her. They both need to consider what their relationship expectations are, and whether they are compatible.
I'm not sure how you found any sexism in my post. If you would clarify exactly what you felt was implied that would require a different approach, then perhaps I can explain my thinking.