Having had a dude hung up on me for a similar amount of time (and he was a friend I once stupidly slept, so he at least had some small reason) and had a stalker (different person) for 5 years, I can tell you that it is creepy as hell even under that situation, so to hear Cullen going on about Amell/Surana in DAI still would definitely be a trigger for me personally. My Inquisitor will be out of there like a shot, and would give my Warden the heads up, LOL! Alistair can deal with him! 
Exactly, I remember about a year after we broke up, my ex tried to get me back and even went so far as to tell me, right after I told the a-hole off, that 'he wasn't going to give up on me' Granted we were in a relationship before that, much farther than Cullen even got with FMage, but it still creeped me the hell out and I was paranoid because he somehow got ahold of my new number and lived in my town. I even blocked him on social media so idk how he got ahold of me. So this type of relationship going on this long would seriously put a dent in his character for me.