I used to have a buddy.
She were both in long term relationships at the time but needed something extra which our partners were not providing.
I saw her on and off for about 18 mths, and the reason it worked was neither of us expected any more than a few laughs and some great sex.
We ended things mutually when she decided to give things a 'proper go' with her partner. That's an important thing to discuss with your buddy, as circumstances change a lot when you are not sharing a normal committed relationship.
I have no regrets, lots of wonderful memories, and an open mind to the idea should the situations arise again. I recommend it
))