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Look, no matter about the other woman (and I won't comment on her because it's typical for us to exaggerate or insult the other girl. Se could be hot for all we know).
He was cheating. He wasn't able to perform for you because he'd already gotten it. It is never your fault he couldn't get hard. And how can you be bad at sex if you never have the damn sex.
He's a cheating, lying jerk who tried to make you feel bad because he only wanted sex from you in the first place and didn't get it because he was trying to have sex with everyone else.
He also probably had erectile issues in general and was taking his impotent related anger out on you