Is AUTHOR wrong in the post ? POST : Reading a lot of these AITA's for relationships has brought up some old memories and I would like peoples opinion on this. Sorry if its long. TLDR at bottom.

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At the time of this incident, I was about 23(m) and she was about 21. Lets call her Sarah. We worked together and she was dating another guy at the office, whom we shall call Tom. We became fast friends. She was into all the nerdy stuff I was into and we got along great. I was attracted to her, but because she had a BF I kept things purely platonic. Eventually she started some flirting. I felt uncomfortable because I knew her boyfriend and he was a really nice guy, and I didn't want to break up any relationship. But I play along in a joking way and try to keep it as friendly as possible.

After a while she started to complain about issues with Tom. He was getting a bit jealous, and in her words ,'controlling'. I let her vent and tried to be as diplomatic as possible. I even defended him at times, saying that while some of the things she was doing may seem innocent to her, they might not seem that way to him. I told her to try and see things from his perspective, and just try to communicate better. She thanked me for being honest, and started saying things like "you're such good listener" and "I wish I had a guy like you". Fast forward a month and she calls me to say they broke up.  She comes over and cries on my shoulder. Now, I would be lying if I said there wasn't a part of me that was happy that they broke up. But again, Tom is a great guy and I do feel bad about the situation. Because of this, I make any moves. 

Over the next couple weeks, the flirting ramps up at work. We do hang out a couple of times, but I haven't made a move yet. There are two reasons for this. Being a nerd, at the time I was very inexperienced with this sort of thing and was nervous. Secondly, my Dad was suffering with cancer, so a lot of my time and thoughts were devoted to helping him and the family. About a week later, my Dad takes a turn for the worst and we rush him to the hospital. He eventually passes away that night. Over the next week, Sarah was now my shoulder to cry on. She even helps out with a couple things for the funeral, which was great. 

The last few weeks been very clandestine at work. Not hiding all the flirting, but not advertising it either. But now a lot of my friends saw us together at the funnel. I later get warnings from a few people that she and Tom broke up because he thought she was cheating on him. Tom even came to me and told me his side of things. Tom is from a very traditional and conservative family, which also contributed to a lot of their issues. I do get a little suspicious, but having now heard both sides of things, I decide that he may just have been overly jealous after all. I spoke with him at length and he gave me his blessing about pursuing things with Sarah, as he was done with her. 

Next time Sarah and I hang out I thank her for everything, I end up making a move and I get shut down. She tells me that she has been seeing someone for a couple of weeks and she they are now official. WTF? All that flirting and she was seeing this other guy while being with me a my Dads funeral? I am obviously upset, but its not like we were together, so I don't get mad or anything. I do feel a little like a fish on a catch a release, but whatever. I don't see her for a few weeks. I wasn't ghosting her, just taking time off to help my Mom get my Dads affairs in order. After that we remain friends, and even start a small band together (it didn't go anywhere, but that had nothing to do with this).  

Over the next six months she breaks up with this guy and starts dating another guy. We all have our suspicions that this new guy started during the last guy. Whatever, not my business. She is still a little flirty sometimes, which I find weird. But I just joke around, ignore anything too flirty and just change the subject. I then start to feel like she is taking advantage of me a little. Always asking for rides, watching her cat for her all the time when she goes out of town to visit family, I even lent her a little money (she did pay me back). But whenever we planned to do things as friends she ends up cancelling because she is too busy. But she still msgs me sometimes and ends up trying to flirt again. At this point I am pretty much done. I don't hate her or anything, just realise that the warnings my friends gave me about her were right and decide to just let the friendship die on its own.

I then find out through the grapevine that she is banging one of my colleagues at work, who is over twice her age, and they have even done it in the office! I didn't believe it at first but one our mutual friends (that Sarah had a falling out with), showed me the messages to her from Sarah, talking about the whole thing. I debate telling her current BF, who I have only met a couple times. But I decide its not my business and leave it be.

A few days later I get a message from her being a flirty again. I snapped. I didn't swear or call her a whore or anything, at least not directly. I just bluntly called her out on all the above shit. How I thought she was a terrible person for leading my on while I was dealing with my Dad passing, screwing over her last three boyfriends, and how it was gross to be having sex with a guy twice her age, in the office. I finished it all by saying that she doesn't owe me an explanation, I'm not her boyfriend, but I just don't want to be associated with her anymore. 

After that, she obviously avoided me at work. I got a new job a few months later, and that was that. She has attempted to make contact on facebook a couple times in the years since, but I have ghosted all her attempts. 

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I do sometimes feel bad about it. I mean, she did deserve it, but I heard from others that she was REALLY upset about it. I sometimes think I may have been too harsh. What do you guys think? Was I the asshole here?

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TLDR; AITA for rather viciously for calling a friend out on being a massive slut?