not enough sex
my wife is 50 and overweight and sick. she cannot have sex as often. I am 53 and started to watch other women more often sometimes wishing sex with them. Is that part of a crisis I am going through? Will it pass? Will our relationship survive? What can I do to stop thinking about other girls? Will that stop?
I assume you are a healthy man, with a normal sex drive. You mention your wife is overweight and sick, which means that even when she is available for sex, it might not be as satisfying as you would like. You may be going through a transition to the 'third age', as you are in your fifties, which is when a this usually happens.
Yes you will get through it. Whether the fantasizing about other women will stop is largely up to you. We project onto women what we need to develop in ourselves, and the time to do so is now. I have a chapter about this in A Harley or My Wife
However, it is likely that you will fantasize about sex with other women for some time. There is nothing wrong or abnormal about this, given your circumstances, but whether you act on it is up to you. Whether you marriage will survive is up to you and your wife as well. Your marriage vows did, I assume, include committing to each other 'in sickness and in health'.