I’ve been friends with this girl for about a year and we both go to the same college and study the same degree. She, however, has a boyfriend and I have a girl who I’m in an open relationship with.
Last night we had a ‘quick catch up dinner’. She told me about all her relationship woes with her boy and that they were on a break (although I know she went out with him the night before).

We ended up back at her place after a few drinks. At about midnight I told her I had to leave. She suddenly said - ‘no, why do you have to go?’ and we ended up kissing.

I told her several times that we shouldn’t be doing it, and tried to leave. In retrospect I must admit that even though I said it 4-5 times and tried to break away, I wasn’t firm enough.

She kept pulling me back and making out some more. She ended up telling me she had a crush on me and has for awhile.

We ended up having sex late in the night. Fortunately, I had a 6:15am college training session that I was expected to attend this morning, so I left after. Now it’s 11:16am in the morning here in sydney and I’m wondering what to do.

I cannot pursue a relationship with her since we've always been friends. I am a student who works full-time and I train for my college sport 12-16hrs each week, there is no time to devote into a proper relationship (the current girl I’m seeing is very casual and we’re honest about it with each other). There are many other reasons too, which made last night a mistake on my part.

I still want to friends with her but I’m at a loss for what to do from here. Should I call her? Msg her? Mention what happened?

Any advice or similar experiences and how they panned out would be a great help.

Well, what happen happen and you can't change that. Both of you are in a relationship with someone, however, you are in an open one.

Now a few things will even happen right now. She will start to feel regret and migh end the friendship with you, or she try to convince herself that the two of you sleeping together never happen, or she move on from this situation and continue being your friend.

Calling her to see her intake on this isn't a bad idea. If the friendship survives this then don't let this happen again.

Yes, it can go many ways, perhaps going to see her soon and talk it over.

But there is no reason you can't move a friendship to a girlfriend, in fact for a lasting real relationship, you are suppoe to be friends with them

You should call her, let her know how you feel about the whole situation. Let her know a few drinks was a few drinks, and what happened wasn't supposed to happen. Tell her you'd love to still be' friends with her, but you're focusing more on your education at this point, and you'd rather not have to worry about a serious relationship. If she gets mad about it then she wasn't a good friend in the first place. If she understands, she's a keeper.

I feel like I should call her, just so she doesn't feel like I've 'bailed' on her.

On the other hand, we never call or message each other usually, and I don't want to mislead her into thinking we've fallen into a relationship mode by calling her the day after we slept together.

I feel like neither of you should be in a relationship before you take this any farther. I don't care for the fact that both of you are in relationships. Whether yours is open or not, her's might not be. There's not any excuses. Just poor judgement. I hope your judgement and choices are better in the future. Meaning, I hope you learn from this.
That's all I have to say.

Have you told your girlfriend what happened?

Isn't that what an 'open relationship' is all about? Being able to sleep with other people?

Be honest with your friend and let her know that you are not interested in pursuing a relationship. Keep it simple.

Time will tell if friendship will happen again.

Ok. My advice is just leave it be. When you see her again behave the same as you always have.
Don't bring it up unless she makes more moves on you and shows that she wants something more.
Then at that time let her know how you feel. Don't call, if it's out of the ordinary.