I echo the comments of those that have applauded the OP for this strength and courage to come here and admit this. I, too, feel that men too often do not stand up for the things that they know are wrong (porn, vasectomy, birth control, etc.) and is most likely swept under the rug.
I can see the connection that has been made between the affair and the vasectomy. The vasectomy opened the door to many things that may not have been considered before. Such is the beauty of NFP. The communication with one’s spouse, the sacredness of the martial embrace, the giving of oneself, totally, faithfully, fruitfully, and freely is HOLY! Theology of the Body does a magnificant job of showing us how this act is sacred and how it renews our wedding vows with our spouse. It shows us that Christ is present during the most special time between a husband and wife.
A vasectomy robs this from you. It takes a part of you that should not have been taken. Your embrace is no longer total, it is no longer fruitful. As the OP mentioned, your spouse becomes an object for your pleasure, not a partner, an object. A way for your to satisfy you temporary need for an orgasm. You would prefer that momentary orgasm to the full enjoyment of what God intended the sexual act to be between a husband and wife.
A vasectomy, birth control and pornography can all be placed on the same scale and measured equally. They all 3 rob the person of something. They take away the part of them that can view their spouse as their partner, as the one that the become one with in the marital act. We hear it every time we attend mass…“Take this…this is My body, which has been given up for you.” As is the case in the marital act, this is your body, given for your spouse, completely, holding nothing back, NOTHING. The pornography, the birth control, the vasectomy, tubes tied, that takes this away. That is holding something back. You are not giving of yourself completely. They all increase the ability to objectify your spouse and use then for your own selfish pleasure.
Sure the thought was that the OP and his wife would have “fun sex” once this happened. Sex on demand. Sex all the time. Then, when sex becomes an act, it loses it’s meaning, it loses it power. It loses the ability to transform us into the one flesh union that God gave us in marriage. Sex is not meant to be fun (it is a byproduct of the act). Sex was not created for your orgasm. Sex was not gifted to us to be great. Sex is HOLY! Giving of ourselves to our spouse as Christ gave Himself for His bride, the Church. FREELY, TOTALLY, FAITHFULLY and FRUITFULLY.
It is not about what you can gain from the marital embrace, it is about what you can give, completely give.