Eh, if he's of an age to have a relationship with Molls, then so's Dresden. If Fitz is the same age as Molly was in Proven Guilty, then she's currently 7-8 years older than him.
Don't really see anything there, but *ahem* (points at his sig), I'm not the most unbiased person out there...
Maybe the "love" angle is the wrong way to look at it. Perhaps seeing someone in her earlier state will help her see the error of her ways (or whatever) and straigten up. Like what happened with Harry, teaching someone younger did a lot for him magically, and personally. Perhaps Fitz will play the same roll for Molly to some degree, bring her back to a connection with others by looking out for him.
Personally I don't think Fitz is going to stick around as far as characters go
I think he was a 1story support character. But if he did stick around it would be neat, I mean he has a LOT of Harry's humor and wit, and sense of Right. I could see Molly responding to that on a base level, and wanting to have him around.