Hrm...what do I post here and in what detail do I go without talking to you in person. Well I'll say this. You're buddy's girl friend reminds me exactly of what I saw (well see now) in my ex-wife. She was very controlling, very insecure, and she also threw guilt in my face at every opportunity. Maybe she didn't do it intentially but she did it. I too was warned and paid no attention. I was in love and that's all I wanted to know and see. Sometimes it's a hard lesson to learn but we eventually learn it. Perhaps it's something she'll grow out of or if he talks to her about it she'll realize it.
With me it got to the point that, while she might have been thinking it was cute, was really pissing me off. I'd bring it up to her constantly but it did no good. It was one of the things that eventually led to us drifting a part in certain ways. Now I'm in no way implying that my divorce was all her fault, it takes two to tango. But had I listened to reason early on I wouldn't have gone through the hell that was a good part of 2002 and all of 2003.
So I'd say sit down with your friend, really hit him in the heart with how you feel. Use me as an example if you want, if we can't learn from our mistakes we're just going to keep making them.
And you're right, we're fortunate being in the truth. If only I did things Jehovah's way I'd be much happier. But you reap what you sow. But talk to him, open his eyes. If he sees it and accepts it that's one thing. But when he's getting called from two stories away to change the channel when the remote is at her feet tell him not to complain.