okay so this is gonna be a long one.

i (now 21F) made a friend on the first day of grad — let’s call her karen (now 22F). we became bestfriends in a few months. both of us were commuters, and it was really fun hanging out with her in the beginning.

come second year, i shifted to residence because commuting was hard (i used local buses while she took the uni bus, which left super late).

that summer, her behavior changed. every time i’d ask to hang out, she’d say she was busy, but i’d see her chilling with others. that rubbed me the wrong way, so i stopped initiating.

we had a mutual friend in class — let’s call her susan (now 20F). during the summer break, susan and i got closer. she had gone through a breakup, her friends were isolating her after a drunken fiasco, and i could relate because of my own friendship drama. so, we just clicked.

important context: originally, karen and i were bestfriends, and karen and susan were close.

when i moved to residence, susan and i naturally got closer — we lived together and were in the same club, while my efforts to stay close with karen were going nowhere. i even asked her twice what was wrong and she didn’t have a real answer.

cut to two days before a club event, karen and i had a big phone fight. she accused me of “stealing” her friend (aka susan), and i was like... huh? when did that happen? she said we made eyes at each other whenever she spoke and that we were isolating her. susan was with me during that call and was just as confused because none of that was happening. like, if i didn’t want to be friends with karen, why would i have tried so hard?

we moved past it — but not really. i still feel like it was unfair for her to pin it all on me when she wasn’t doing anything to maintain the friendship either.

fast forward to february. my bf (25M, now ex) left for work. he was introduced to me by karen — they were super close, like siblings (not biologically).

karen had confided in me about this long-distance situationship she was in. they hadn’t done anything except sexting, but she was serious about him and said she wanted to introduce him to her parents someday.

now, my bf’s group had another guy who joined because he’d dated someone from it. the breakup was messy, and the girl had been isolated — though later it came out she wasn’t at fault. around nov/dec, karen started talking to this guy and things got physical (not sex, but still). so yeah, she basically cheated on the ldr guy. a few months later, she decided she didn’t want to wait for the ldr guy anymore and also didn’t want anything to do with the other guy — partly out of guilt, because his ex had helped her out during a tough time. so, it ended.

she got with another guy later, but that’s irrelevant here.

as her bestfriend, she asked me not to tell my bf about this lil cheating situation — it would cause problems, especially if the ex found out karen had gotten physical with her ex, since she’d be ostracised or whatever. i told her not to worry.

then in june, susan and i had a fallout over something we just couldn’t see eye to eye on. after that, karen lowkey took her side — not obviously, but she had told me earlier she’d be “diplomatic” in our last year, so i guess that’s what she meant. around this time, her childhood bestfriend removed me from all socials. and that’s when it clicked — back when grad started, karen had talked shit about this same bestfriend and told me not to accept her follow requests. and now she was doing the exact same thing to me. still, i kept her secret. not mine to tell, right?

cut to december — her sister’s wedding. we’d talked about this since year one. her family knows me, and even her mom asked why i wasn’t invited to the engagement. (nothing bad had happened between us at that point.) during the wedding, her mom again asked about inviting me — my ex heard this happen. so yeah, she could’ve fixed things if she wanted to, but didn’t. and that’s when i realised she never really saw me as a friend. so i decided to stop caring.

later, while going through wedding pics with my ex (we were just friends by then), i saw the guy she cheated with. couldn’t hide my reaction. he asked how i knew him, i made excuses, he kept pressing. and that’s when i realised there’s no point in keeping her secret when she clearly didn’t care about me. so i told him. he was shocked.

i told him not to tell anyone or let it slip that he knew.

a few days later, karen confessed the whole thing to her brother (who’s also in the group). he banned the guy from their place. then she asked her brother, “my ex knew about it right?” and the brother accidentally said yes (yeah, my ex couldn't help but boast that he had already known). he tried to backtrack by saying it was recent, but karen decided to play victim and claimed i must’ve told him months ago.

where am i at fault here? or is it my fault? i need advice and to make sense of this situation. like, what could possibly have made her go from point A to Z like that?