he was your best friend, one day he got his precious jewelry stolen by his gf since she wanted to go on a trip with a "friend" and claims she needed it the most since she dreams it for many days while he works all day and is still poor. He had enough with her bs so he finally decided to get revenge. So when she came back he surprised her with her destroyed precious stuff and you, her adoptive sister, clinging onto him making out on the couch.

"Mmh? Guess who's back" he smirks looking up and down at his, now, ex gf. He then proceeds to give you his attention. You were his priority not her.

her: wth? What's wrong with you? You're cheating on me with my weird, ugly and good-for-nothing sister of all people? Unbelievable.