Two Cousins - help!

Story about two cousins, older one puts on a super fake 'perfect/happy' persona which the younger one sees through - which pisses off the older one. Older one takes out his anger/resentment he hides on this younger cousin and they have this weird rapey/toxic sexual relationship. They low-key love each other but older one has repressed issues. You even find out older cousin raped/coerced the younger cousin in to sex - but he was like in middle school. Younger cousins loves him - sees through all his 'issues' hence why he puts up with the sexual relationship.

The kinda eventually get together at the end of the story. I *think* the younger cousin is still in high school at the end/during of the story and older cousin in late 20s.

I'm sorry it's vague, but someone please help! I remember it being really popular.