I'm in a similar postition. I know I am BF whose name starts with A's rebound relationship after his marriage. He is mono, we were friends and fell in love.
He knew that I wouldn't be leaving my husband. However, wanted to continue the relationship. A few weeks ago, after I talked to him about some long term issues I had with hubs, told him I wanted a d in the heat of the moment. He apparently, felt that I would follow through with this and I would begin a permanet ltr mono relationship with him. I told Husband this and that I would straighten this out. A and I had a long talk, almost broke up.
I explained to for several reasons we couldn't be togather long term. We have decided to proceed with a quality not quanity relationship. We both feel this is where we are now and when he is ready to move on. We will transition to friends. He isn't currently looking for another partner, we have good understanding of this. I just know for me, my life is better with him in it and I love him. So I am doing my best to meet his emotional needs and my husband's needs. I am just not going to worry about how long it lasts. I do realize we aren't on a day to day thing. We both have plans for future things togather. So I am happy and secure. I also know he will always have love in his heart for me.