Regarding whether protestations of love are manipulative or honest, context is everything.
If I'm in a relationship with somebody where love might have grown as a result, then I can tell that person.
BUT
Nobody just says, "I wanted you to know I love you. Anyway, back to our discussion about tibetan prayer wheels."
"I want you to know I love you" is implicitly one of those folded-up notes from 7th grade saying "I love you. Check a box. [ ] I love you too, and not as a friend [ ] I don't love you, or I love you like a friend or somesuch BS" The subject is forced to respond, either by saying, "REALLY?!? <3 <3 <3 I've loved you too for a while! I can't believe it!" or "Uh. [Insert uncomfortable acknowledgement of weak to nonexistent feelings]"
To say it to somebody you aren't close to and don't spend much time with seems immature to me. I mean, Sven may BE emotionally stunted. I dunno. To pop this without at least acknowledging that he F***ed up but it will never happen again is bad salesmanship or something. I know if I were Faye, my first question would be "If you love me so much, why did you cheat on me? Did you love me less then? How does that work?"
I will say again that Faye's defining characteristic seems to be anger. This, to me, disqualifies her from GF material. Concealing your hostility behind jokes is one of the first jackass tactics. "I was just kidding when I made you feel small" Relationships are hard enough without having a partner whose toolbox has a lot of big hammers.