Communication, communication, communication.
Talk to each other.
Now to be honest, when my wife informed me we had started this journey, all I asked her was if she had enjoyed herself. She couldn’t look at me when she said yes. I told her good and that I loved her. A few days later I told her I was ok if she was with him again, and the next day she told me she had been with him again.
We talk frequently to make sure that everything is still going good between us.