I slept with my best friend, is there anyway to remain friends?

So I have been friends with this one girl for about 9 years, as part of a mixed group of 8 we would regularly go on holiday together and see each other every week. She is generally a flirty girl but me and her were always closer than most and would usually end up pairing off together or sitting next to each other when we went out.

More recently we started spending alot of time together outside of the group, texting each other everyday, going to the cinema etc. I was single and whilst she had a bf he showed her no interest, so I think we both just enjoyed the closeness to someone. I guess it was obvious by this point we both had feelings for each other, but I was perfectly happy being friends.

When I moved into my house she would join me on an evening to chill and watch a movie or something cuddled up on the sofa and then she would sleep in the spare room. I often asked if it bothered her bf, but she said he didn’t mind. I did think at one point she was simply coming to mine to try and make him jealous to show her that he cared.

Then after a while she told me she fancied me and wasn’t sure what she wanted. On holiday that summer we ended up kissing one evening, she would tell me how she would ‘manipulate’ the group so we could play strip games or end up drinking shots off of each other for example to be close sexually to me, her justification was if it was part of a group it wasn’t really cheating.

It culminated in us spending New years eve together at my house party, we stole a kiss at midnight and she spent the night in my bed.

After this she began backing away completely, we went from texting everyday to her barely responding. I knew she felt guilty and we both knew someone had to end it so i didn't push it, but I just wished considering how close we were it could have been discussed maturely with our cards on the table. Everytime I tried to talk to her she cut me down and would accuse me of making a drama out of it. I think she expected me to declare my undying love for her but all I really wanted was closure.

6 months later we still hang out with our group of friends, however the smallest thing will lead to an argument in front of everyone. I am often concerned that our arguments make it awkard for the others so back down to keep the peace but as they do not know we kissed and therefore the underlying reasons for our arguments, I always come off worse and in the wrong.

I do not want to lose our shared friends so can’t cut her out completely, I still enjoy hanging out with them and something keeps pushing me to make the effort with her, however if I send her a casual text, I barely get a response or see any kind of effort from her.

Basically I was wondering if anyone had been in a similar situation? Any advise of what I can do?

‘Karma’ & ‘its what I deserve for kissing another mans girlfriend’ are both valid responses, but believe me I already know what I did was wrong and deserve at least some pain!!!