Guy99, you have been given sensible advice, and you seem to have great self insight.
Just another thought to add to the mix, and you dont have to answer, but think about it.
Very few women are going to chose a life without any children of their own.
In your next relationship, will you look for a woman like this who is adamant that she will not want, or cannot have, children? (She may chance her mind a few years down the line, when she is happy and secure in your relationship)Or will you look for a woman who has a family already, and effectively become the step dad to your new partners kids. (You will still get the "oh, can I get them into a good school/university" discussions then)
I have a friend who at the age of 18 declared she did not want kids. 20 years later she has not changed her mind. She has always been upfront with any man she has met, to ensure she would not waste time on a relationship where the man would want children. Her last relationship ended a few years ago when her partner of ten years decided he wanted children after all, and set out to find a woman who in her late 30s did not have children allready, and were keen to settle down and start a family. (He is still looking). My friend is ok-ish, she got over the relationship, it was after all "just a man", she has her cats, she will be 40 next year, she is the aunt of 5 nieces and nephews she rarely sees, but has her cabriolet and her career in finance, and her horse.
My point is: People change. Goalposts change. And people think others will change, or that they can change others. If you are sure you will never want children, and you have analyzed your motives for not wanting kids and you are certain they are valied and longterm, I agree you should have a vasectomy.
You need to ensure not only that you dont waste the time of a woman of childbearing age who wants children but think you will change when you have been with eachother long enough, but also that you dont end up sad and lonely when your next partner decides a life without children is not for her after all. Especially if she is much younger than you.
My other friend left her 60 year old partner at the age of 35 when her biological clock started ticking, after over 8 years together. He was devastated. He said: "Who would want a sixty year old ugly sod?"
My first friend is now considering getting a dog to avoid the void after her partner left. Two cats and a horse (and a sportscar)is not enough, clearly. And at the age of nearly 40, she has a hard time finding a man who is neither
a) divorced and with children;
b) still single and living with mum;
c) unable to form any relationship - ie total twat
Second point: You need to weigh up carefully what you want in your life and with your future. Do you really want to give up on life with a woman you love, just to avoid fathering her children. And what is the alternative future for you?