At the same time, however, I do take some issue with
@RDKirk 's assertion that you can train yourself to be attracted to anything...that it's merely a matter of will and the desire to do so.
One thing I look at is that it is important to distinguish between initial selection of a spouse, and living with the changes life brings.
To a degree attraction is biologically driven. People on the whole find indicators of health and fertility attractive. As you have said before, there is a generally acceptable range for most guys. And you have to go pretty far along to the skinny or overweight side for a lot of guys to get worked up over it.
For when you are choosing a spouse, I think people should obviously marry someone they find attractive. Now in this case the poster indicated he did not think this through in that way because the intention was not marriage. They were not believers at the time, they had sex and she was pregnant so they married.
And he has rightly assessed that once you are married you should stay married. And he has desired to find his wife attractive.
Many things can happen in life that change the appearance or physical ability of a spouse, so it is good to try to adapt one's thinking out of love for your spouse.
I did mention earlier in the thread that there are issues with extreme obesity that do make it hard to deal with. Some of these deal with safety as well. But even within that framework, one should try to work with their spouse because they love them.
And as to how to encourage a spouse to lose weight, that is a tough question.
I agree with all so far that in this case his wife is trying to lose weight, is not extremely over weight, has legitimate health issues that have contributed, etc.
And the poster has acknowledged that as well. I think the big question for the OP is whether appearance is actually the only factor.
If it is, then
a. turn out the lights
b. find a part you like and look at that
c. wear a blindfold
More likely there are factors just beyond the appearance. And some may be more about him than her.