Demented? I don't know where you get that from.
But Bella being nearly twice MC's age and things starting to sag after a while, you're saying that like it's a bad thing. There re guys out there that much prefer older women over girls their own age. Jason Momoa is married to a much older woman than he is, Madonna has boyfriends/lovers more than half her age and so forth, so, what was the issue again?
![Stick out tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Just because Bella is much older than MC doesn't mean the relationship can't work out in the long run.