Basically there's two friends who I've been close with for awhile, one is C who I've known longest and the other is J who I met about 8 months ago and brought into our circle of friends. C is usually a chill guy but pretty quiet about his personal life, J is a pretty quirky gal and we've always gotten along great. Going back a few weeks a spark lit between J and I which quickly turned into dating and honestly I've been happy but when I told C he got upset and angry with me. Turns out him and J had a brief thing a few months ago but never told anyone, things didn't work out because J felt they were incompatible romantically and they moved on agreeing to be friends. He still has feelings for her and when he  told me this I went and confronted J, she said that she viewed it as a mistake because she'd have rather kept him as a close friend.  When I talked to C I told him that I was sorry if me and J being together made him upset but I really like her and if he wants to remain friends he'd need to accept it, he then threw a fit about how I'm an ass who doesn't care about his friends feelings. He quickly apologized the next day but damage was done. 

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So AITA?