Hey so I need some advice on what to do here.

I've been in an open relationship with a girl for almost 5 years now. We'll call her S. She's awesome. This relationship is very committed despite the fact that I'm permitted to be with other women casually.

Part of the reason that the dynamic is this way, is we're both young (23/24) and I travel extensively for work and with my band. I can be gone sometimes 7 months out of the year.

So this time I was living in Detroit for 6 weeks from November to the end of December for a work thing, and I thought I'd use it as time to work on my game and see if I could make anything happen with anyone. It was successful. I had a few tinder dates that went well, and then I also ended up hooking up with one girl I worked with, and also the girl that works at the front desk at my hotel. We'll call this girl K.

It was pretty cool for a week. K and I saw each other every night that week but it was my last week in the city. I told her I'd come back in about 10 days to see her because I only live about 4 hours from Detroit.

So I did and we stayed together for another 3 days in hotels and it was a really nice, intimate time. I guess I could have been more adamant about the fact that it wasn't going to continue once I left. In retrospect I was pretty ambiguous. This was my first mistake. But she was just so cute. And also I've been feeling the sex in my long-term relationship is a little less exciting than I'd like it to be, as S doesn't have the most colourful sexual palette. We've learned this over time, and I don't expect her to be more adventurous.

So fast forward to now, and since the day I left I've been having serious trouble ending things with K. When I told her I couldn't be in a committed relationship with her, she had a breakdown. Keep in mind we'd seen each other a total of maybe 8 or 9 times over the span of two weeks and that's it.

My problem is this: K hopes that we'll be together in the future, but we won't. She's so upset that she's just gone nuts. Evidently she's always been nuts. She's cutting her thighs which apparently she hasn't done in over a year. It's really disturbing and makes me feel horrible to be the cause of that. She's also drinking and violating her probation from her DUI.

So I don't know what to do really. I'm completely at a loss, and normally I'd talk to S about this stuff, but because of the conflict of interest, I don't think that's the right way to go.

Guys, how do I break up with someone I'm not even with, and do it in a way that she doesn't destroy her beautiful self? This is fucked. I'm worried she's going to seriously injure herself and/or fuck up her life. I feel like I'm being blackmailed.