Oh yeah, I can relate.
It's like a bad joke. She's easily put on 40 pounds since we became a couple. She was always a little thick, but was attractive. She has a very beautiful face and spectacular naturals, but she has put on a lot of weight in the mid section, and legs and ass. So much so that I avert my eyes when she's nude because it's a boner wrecker. Under the covers is all fine and dandy, but I'm a visual guy and the visual just isn't good. As a result, in order to get it up, I've turned to priming the pump with some fairly out there fantasies (all of it legal and I won't bore you with the details.). Also, the sex has become more perfunctory because I just don't want to look at the rolls. This is not how I like to have sex. To her credit, she has her head on straight and is perfect in just about every other way. But you always want what you don't have don't you.
Now myself, I've recently lost about 30 pounds by removing all sugar from my diet. I'm 6-3 and have dropped from 250 or more to 220, with a goal of 200.. She has noticed my weight loss (and most notably that my clothes don't fit and I make a point of showing her) and she is well aware that she is too fat. So she has been eating healthier. In fact, we always eat a healthy evening meal. I have watched what she eats and I have to say that she has a portion problem. She simply eats too much. She may have lost 5 pounds. A start, but a long way to go.
So she is trying, and I keep after her (gently) about portion control and walking more for exercise. Still, she has a long way to go. I would never trade her in for another woman, so I'm just going to keep encouraging her to watch her diet and walk more.