Relatively speaking

My wife's longest term guy was my older brother. We were around 40 at the time and he was going through a divorce and lived nearby. They got together a few times before she told me about it. Once I got my head wrapped around the idea they kept going only we didn’t tell him I was aware it was going on for most of the relationship. Once we told him I knew he ended it not long after saying he felt too guilty. But a couple years later he came back on occasion. It was the like an open secret where we all knew it happened but wasn’t discussed between us. I just gave them the space to play if they wanted the opportunity and when it was over we all just acted like nothing went on. Until he left or she came back to me, then it wasn’t long before I added mine to his.