Most times selfish women NEVER come back to you in a healthy relationship between just the two of you. Especially when his cock was so much bigger than yours. Unfortunately for this fellow she is ruined for cocks his size from now on. That's just the way it is internally with a woman. She will always crave that cock pushing up against her cervix and into her abdomen.
I love it when posters generalize with absolute certainty from one personal experience.
I have had the luck of having been able to give pleasure to wives, most of the time with their husbands present and watching, regularly since I was in my late teens. I have a lot of experience. Every couple is different and sexuality and the feelings that surround it can be complex. However, I will tell you a few things that I have observed:
Out of dozens and dozens of couples, the wives of which I have satisfied (needless to say, I have the equipment and really know how to satisfy women), I can count on the fingers of one hand the number that broke up because of our sex. Many of my relationships with my couples lasted for a year or more.
It is very rare that a woman will agree to fuck another man before she really feels that she is unsatisfied. For her to choose the pleasure of a big cock over her husband's small one, she has to know that she needs it. Its not the fault of the sharing that makes her want bigger. She has wanted it long before she agrees to have me.
People's anatomy is different. Not all wives want a bigger cock. But those who are unsatisfied by their hubs inadequacy are either going to live frustrated, getting more and more angry, until they have affairs, or they can choose to have someone like me satisfy them.
I would never think of breaking up a relationship. I love the pleasure I can give to an unsatisfied wife, and the envy of the hub also adds to things.
But don't think he doesn't love it. For men in these relationships, seeing their wife in sexual ecstasy, being fucked by a powerful man with a big cock, is a total turn on, as well as being painful at the same time. I don't claim to understand it, but it works for both the hub and wife.
This kind of sex may not suit your taste, but it certainly gives loads of pleasure to lots of couples. My experience proves that. Get over your self-satisfaction, and accept that people may be very different from you, and still have exciting and satisfying sex lives... and married lives.