This was in my high school and early college years, later on in life I was able develop romantic relationships with them and healthy platonic relationships. I’ll be upfront and say a lot of the times if a straight dude hates women vehemently, it’s probably because he’s not getting laid or able to form any semblance of a romance with a woman.
In general, lesbian sexual attraction is not seen as valid or "real" due to, you know, patriarchy and homophobia. Women cannot be defined outside of a relationship to a man. This is why girls can kiss each other while wasted and it's not seen as gay (or even as cheating if they both have boyfriends), but a dude would be labeled a homosexual the instant he brushed his buddy's hand. It's why couples look on lesbian Tinder for a female third and not nearly as often for a gay male one. And men will routinely solicit threesomes from monogamous lesbian couples, so honestly, them coming onto me while I'm single is pretty mild in comparison. On some level, yes, they really do not believe that exclusive attraction to women can exist - that's the belief held by our culture at large - and that's why all those "friendships" immediately ended.