I feel the same. Everyone's saying how Leo acts like a psycho, and yes, he does go off the deep end to be fair, but he hasn't exactly been treated fairly in the past.
SPOILERS BELOW!!
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I mean, Leo is obsessed with Chase. Is it because he actually does have an otter fetish? Who knows, but I interpreted the scene with his porn stash more indicating that he's looking for smut he can insert Chase and himself into, rather than him only liking Chase's appearance.
But for Chase to go do THAT to him? He knows he is jealous and insecure. So he thinks it would be funny to pretend he was pissing off with another guy as a JOKE? And learning Jenna was in on it too? Not only that, having Jenna always trying to one-up, or straight-up belittle him when he's trying to impress the guy he's into? Chase kind of ending the relationship, but never actually ending it also fucked Leo up. He's left wondering "Are we? Are we not?" Only in Leo's good ending where Chase actually ends things does Leo actually start doing the healthy thing and move on. He needed to end it sooner, not just leave him in relationship limbo for years. It's no wonder Chase and Jenna aren't my favourite.