The most difficult part of a relationship, I think, is growing together. There are no doubt a ton of moments in that together direction where outside or inside forces will be making you feel like you're growing apart instead of forward. If your partner feels you've gotten fat, and that's impacting the mojo, so to speak, within the confines of your honest marriage, the two of you should talk about it. You'll start by laying out what seems like a reasonable grievance to them,. then, in less than five minutes, you'll be screaming at the top of your lungs for help.