Hi, I think there needs to be intimacy in a marriage. I am talking about the bigger meaning of intimacy, not just sex (which is merely an offshoot of the overall intimacy a couple feels.) It sounds like you are talking about sex only, and complaining that it has left your marriage. (In fact, it sounds like you are saying that if there is no sex, the partner who wants it can justify leaving on the basis that it is "medically" draining and painful. I'd suggest that throwing "medical" into the mix does not add strength to the argument. It's not really medically a problem.)
If intimacy has faded in a marriage, it's often due to reduced connection. This can come from a couple having chosen each other to marry without really assessing whether they were a good match, but more often it comes from people being stressed and overworked. Sometimes it comes when one person is expected to do more work than the other, especially if their assigned jobs are the less-interesting and constant work (like the woman expected to hold down an outside job while doing all the housework and child care). If someone is in a marriage where they both still communicate sweetly with each other and care about each other, even if the sex has fallen away because of stress and exhaustion, the couple might not want to dissolve the marriage. Also, such things are often temporary. Couples can go through difficult times and find that they have a renaissance in their love for each other once the harder times are past or the kids are off to school.
I believe this is a personal question. For some, they can have emotional intimacy that parallels or even trumps physical intimacy. For others, this would be unacceptable. Marriage is not a one size fits all proposition and couples can define it any way that works best for them. Happy can look different to different people. But if you are unhappy with a relationship lacking intimacy, then it's not the right relationship for you. good luck