When they hinted she killed herself over Woo Il, I thought that was a reach. But the later explanation made it slightly more believable, although I didn't love it either. 

She has an unrequited love for her boss. In a drunken night, she ends up sleeping with his best friend and, if we're honest, she didn't look like she was too pleased with him kissing her.  And the next morning while in the car, she definitely looks devastated over what occurred. Then she finds out the guy she likes knows. Embarrassment. Then her boss's sister, who he adores, attempts suicide right in front of her because Ji Hye slept with Woo Il.  Hwan Ki had been cold to her that day, didn't talk to her, doesn't answer her calls afterwards. So she's probably thinking he hates her because she hurt his sister who attempted suicide right in front of her. Plus the shame of sleeping with a guy she didn't like. The shame she'd have endure when she tells her parents why she quit/was fired ('cause, there's no way she would've remained employed after that even if she'd survived; her job was over). 

So... I guess I can see it. But personally I think it was too rushed. Maybe if days had gone by. Maybe if Yi Soo had been harsher. If Woo Il had been a predator who was sober not drunk during that night. If something more was going on with her, maybe an undiagnosed mental illness. It could've worked but I guess they didn't want to go too dark, which is a shame because they were already broaching a serious topic with suicide. 

I thought that the sex with Woo Il was most definitely Non-consesual bordering on outright rape, if I was Woo Il whether drunk I would be aware she had no interest in sleeping with him, just because she didn't fight or say anything doesn't make it consensual. My view was it was rape and I google this because it annoyed me and there are alot who agree. So that plus all the stuff mentioned above.

Also unfortunately suicide is normal, it's happens alot and sometimes it is hard to see why someone does it. If in this situation she clearly had some social anxiety or something plus mentioned above in it's rape I can understand more than if she was just embarrassed.

Gotta be honest this messed with my head enough not understanding enough and realizing little things can push some people to extreme actions, and made me realise I myself needed to talk to someone