>>1
I believe you know that "nice guys finish last". How they never get ladies. Well, during a discussion (you'll need to do that on a day they had a slight altercation and she's already worked up a little), talk about him. Describe how he acts and reframe his behaviour as being the one of a kind, but insecure "nice guy". Use anything she gives you. "Oh, he does that, but that's because he loves you too much and doesn't know how to handle this, so he's being afraid that you might leave him because you mean everything to him and he can't leave without you". Add emphasis on the insecure issues, and how you are not. You'll seem to be understanding and praising him, when in fact you are subconsciously reducing his "mating value".

Now, I don't condone these techniques and think you probably are a nasty person. Also, keep in mind that if she's able to be talked in leaving him, she'll probably be able to be talked in leaving you.