TL;DR at the bottom. I'd suggest reading everything though to get the full picture.

EDIT: Fuck, message received. Apparently a girl turning 20 in a month is too young for someone who's 28. Nice to know that I'm just as bad as child predators or something. You can stop reading this, it's clear that something I'm really struggling with doesn't matter even though we're two consenting adults. This was a mistake.

My coworker (19F) has a boyfriend (19M) for about 5 years now. The guy is controlling, manipilative and abusive. I'm talking about checking her location at all times, forbidding her to go out or friends (especially not guys) and checking her entire phone and social media accounts. Literally no one has approved of their relationship, not her parents, other family, her friends, other coworkers and so on. He has threatened with things like suicide, leaking private photos and sharing her secrets with others if she ever decides to break up with him. I've seen her cry so much that it just breaks my heart. And these things are just the tip of the iceberg; there's a LOT more of which I could write a whole book if I wanted.

For a few months now there have been certain 'tensions' between me (28M) and her, both on and off the workplace. And a few weeks ago, some other coworkers convinced her to go out against her boyfriend's demands. I decided to go as well when they asked me to come. The entire night my colleague was bombarded by texts and phone calls, demanding her to go home. She denied, and we all slept at another colleague's place. I shared a room with her, and after months of flirting we finally made out. The following weeks we both developed feelings for each other. We called each other every day for hours, and we were both on each other's mind all day. She decided by herself to talk with her current boyfriend, but I received the same answer twice: "We're going to try and make it work." Yet we still had a spark that just wouldn't fade.

We saw each other today, just before she was leaving to go to him again. We shared the same loveydovey crap we always did up until that point. 2 hours later, I received a text. "We're done. We talked, and we're going to work it out." Obviously, I was devastated. Not just because she wasn't going for me, but mainly because she decided to stay with HIM. She's missing out on so much of her life right now. I just wish she would put an end to it, whether she chooses to stay with me or not. I replied to her that I respect her decision, even though I believe it's a mistake. And obviously that I still have feelings for her which won't go away that easily.

I (and her friends/coworkers as well) genuinely believe that this is her boyfriend deciding for her instead of herself. I'm afraid that he is threatening her like he did before with all sorts of consequences.

In her case, is there something she can do to leave him without consequences? Is there some way others like me, friends or coworkers can help her with this? And in my case: Is this worth holding on to? I don't believe that in the span of two hours, all feelings she had for me would just go up in smoke. What are the things I should and shouldn't do? I'm wide awake for 7 hours now and getting pretty desperate.

TL;DR Coworker has a toxic and abusive boyfriend, we (kind of) started dating and developed feelings for each other, but in the end can't get herself to break up with her current boyfriend due to various (possible) reasons. What should I do?