Chubby Trapped
When your significant other gains "relationship weight" because they are no longer trying to attract a mate. If you are too deep into a serious relationship to dump the person based on appearance, you have just been chubby trapped.
Guy 1 "My girlfriend stopped going to the gym because she thinks we are going to spend the rest of our lives together."
Guy 2 "Ah man! sounds like you've been chubby trapped."
Guy 2 "Ah man! sounds like you've been chubby trapped."