Belle was being absolutely ridiculous - he pecked Anna as a mate, surely you would rather your boyfriend want to marry you than snog you?
The way she went off at him was proper unhinged banshee, yelling the same thing over and over again not letting him speak, then we he refused to react and walked out yelling "WALK AWAY DEN YEAH WALK AWAY", it's so trashy and TOWIE-like. I don't blame him for thinking "yep, not for me" and ending it! Would be total red flag for me, although I can't imagine my chilled-out husband doing that haha.