I suppose each couple have different thoughts and experiences. For us i have not regretted it for a single moment.
My wife had a lot of Black lovers before we met and to cut a very long story short, she continued after we married with my full encouragement.
Eventually, she started seeing one Man on a regular basis and spoke to me in private telling me she wanted to stop as she was falling in love with him. Of course, I encouraged her to continue but begged her not to leave me for him as I loved (and still do) her.
She said we were playing a very dangerous game but she would continue on the basis that i agreed. She also wanted to spend more time with him alone and go away for weekends with him etc. Again, I was more than ok with this.
Regarding the feelings i had, the changed throughout their 3 years together.
At first it was exciting for me. I was hard all the time. When she come home to me i could not keep my hands (and dick) off her).
She started looking after herself. She lost weight. She dressed more classy for him. She went to get her hair done more often and she was "different". She also had me do more things around the house like washing, ironing, cleaning etc. I also looked after our baby more.
The fact that she did all the above actually made he hotter if that was possible. She did fall in love with him and told me so. I remember that chat as if it was right now. She said "you know that i love Omar and i will never stop seeing him even if you want me to. Dont make me chose between you both as you will lose".
The funny thing is, after this chat (which went on for a couple of hours), i loved her even more. I got hard and she gave me a hand job but also said the "Omar want us to stop having full sex". I was shocked but found it very erotic and understood his point of view 100% so we stopped. I was allowed to eat her, cuddle her and make her cum with my fingers but never full sex.
The upshot of this was that i started having erection problems which, in a funny sort of way, made me even want her more.
Perhaps i am just odd, but we are still together after 20 years of marriage and love each other. She is THE ONE for me.
Not sure if my rantings help to answer anything lol