I’m a bisexual woman, and I find it offensive for pretty much the reasons he said. Like some people said up thread, men tend to think sex is all about them and their dicks. That’s why there’s this concept of bi women as basically just sexually adventurous straight girls - people think of bi women kissing other women while their boyfriends watch, or having threesomes, or having flings with women before settling down with a man. Girl-on-girl isn’t seen as threatening to heterosexual relationships because it isn’t thought of as real, not like sex with a man. But bisexuality isn’t heterosexuality with a cherry on top. My feelings for/relationships with women are real, every bit as genuine as my feelings for/relationships with men, so of course the cheating would be real too. I find it insulting when people say it’s not.