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?

Just because Bella is much older than MC doesn't mean the relationship can't work out in the long run.