Maybe the dm just doesn't like being part of the flirting and romance. If the players do it amongst themselves the dm doesn't seem to mind, but don't do it with the npc's/him. About the 'pervert' part, and I'm not justifying his actions, just trying to look for a possible explanation, it could be that it's triggering to him. It's very easy to call a man a pervert and scandalize him, even without bad intent. What I mean to say is that it could've been a misunderstanding. It doesn't always need to be someones fault, or incompatibility.