Are you trying to say that Quentin could possibly ever forget Amanda and put her completely behind him? No! No, no, no!! That would be like saying that if Barnabas and Angelique would have somehow gotten together again after his declaration that she was always his one true love (which we know damn well they would have) they would have never lasted as a couple because they would have surely killed each other - again. No! No, no, no!! Such beliefs are tantamount to blasphemy!! Blasphemy, I say!!!!
The only way Quentin's belief that Daphne had become his true love makes sense, and sense within canon, is if he'd been fooling himself because the pain of Amanda's absence had just become too much for him to bare and he could endure it no longer. Or if he had been listening to Stephen Stills' 1970 song
Love The One You're With too much:
"And if you can't be with the one you love, honey
Love the one you're with
You gotta love the one you're with
You gotta love the one you're with
Oh yea oh yea, yea"
and taken it to heart - or some other region of his person.