It sounds like you had a vulnerable moment and, with the addition of alcohol, found yourself in a situation that felt good at the time. This is completely understandable and I don’t feel you are guilty of anything.
It also sounds like the kiss was mutual and that you may have been receiving signals beforehand when she placed her hand on your leg. There is no blame here.
Alcohol blurs the senses and we often behave in a manner that is not our normality. For this reason I think you need to first of all forgive yourself for the whole thing.
The break-up of a relationship can be very difficult to deal with and it is easy to see how the attention of another female could ease your pain at the time. It seems your colleague is feeling rejected and this is something she will have to deal with herself. You are not responsible for her anger or resentment.
Starting a relationship with a married woman is the last thing you need right now and your colleague must realise this. For now, the best thing to do is to maintain distance between you both and if your colleagues continue to ask questions, maybe steer them in her direction. This might alert her to the fact her behaviour is making the whole thing obvious to others and in turn, encourage her to be less resentful.