literally why does 似合う keep breaking my brain

ok so i keep trying to use 似合う when i wanna say like oh that shirt looks good on you but then my brain MELTS because of 似る and 合う like are they the same?? and then there is 互 for some reason?? i saw 互 on some sign for a store or maybe it was like 女性 anyway i totally forgot if i was supposed to use 似合う for people or clothes or both and now im just staring at my flashcards wanting to cry lol wait what was my question a