Oh dear. I am reading about myself about ten years ago - and it's chilling how similar it sounds. Yes, I was willing to overlook a shove, because it was only a shove, no bruises or anything like that. I couldn't talk to, or about, any other men - but that was ok, yes?, because he was being manly and really wanted me to adore him the way he adored me. The little shoves became a bit harder, and I even got the occasional slap, but I could overlook that - because sometimes, we had a lot of fun together, and it was probably me annoying him anyway. He'd get all sulky if I wanted to see any friends or family, but that was ok too - after all, it was him and me against the world, wasn't it?. Friends are only bad influences, who needs them anyway?
Geeklover - your friend needs you. Please do whatever you can to stop this slippery slope that we can all see unfolding before our eyes. She may not welcome your input (I wouldn't have), but she needs to know that you'll be there to pick up the pieces with her when this all goes horribly wrong, which it will. Every single red flag is flying here - your instinct may be to walk away, and I understand why - but please be a constant in the background for her, even when she rejects you and lets you down, as I think she will.
Geeklover's friend - if you are reading this, please be aware of the signs that the rest of us can see so clearly. You are only a month in, and it's so easy to walk away at this point. Not so a few years down the line, when perhaps you're more financially invested or, God forbid, with Dc's. Be on your own for a bit, it's fab to take some time out to reflect on what you want, draw up your own boundaries, and just be yourself with your friends. I really wish you all the best.