best way to end this?

Please keep anon

Okay, i did a pretty douchey thing, Last night i slept with my flatmate, we stopped this morning so i could go to a lecture and whilst in lecture she text me and invited me round to her room straight after my lecture. I went and we slept together again until this evening.

I left her room to go to work and as i left the flat she came outside and started kissing me goodbye.

Now she is sending me sex texts, telling me she had been attracted to me for ages and inviting me over to her room again.

I cannot say it was a one time drunken thing because i went back today sober after last night, she is a nice enough girl, but i really don't want a relationship and it feels like she does at the very least she wants to see more of me.

Now i know what its like to have feelings for someone and not feel them returned and i can only imagine that negative feeling would be amplified if you slept with that person only to find out the feelings where still not returned and i rightly so feel like a complete ****.

So what would you suggest would be the best way to end this situation fast,

Tell her it was a mistake, admit I'm a dick and apoligise?
Try to sugar coat it and apoligise?


or any other ideas?

I don't want to leave it too long so that she might build up ideas or anything because i am just not looking for anything like a relationship.