he proposed after about 3 months when he was drunk and has just bumbled along with it because he can't stand up to her
Has he actually told you this and he didn't mean to propose/made a mistake? Or are you just guessing this/talking about it behind his back?
I'm just wondering if your friend's fiancée has picked up on you all talking about how doomed the marriage will be and that's the real recent you've been uninvited to the ceremony?
He's told us that he proposed when drunk and didn't really mean it, and his response to being asked why he was still going ahead with it was "well you know what she's like." And we do.
Nobody's said anything in her presence about how we feel about her/the marriage so she doesn't know his friends.
There is definite emotional abuse, I have seen one occasion of physical violence from her towards him about a year ago (I don't mean to dripfeed, but it's been asked upthread) - he was drunk at a party and had fallen asleep so she kicked him several times to wake him
, we told her in no uncertain terms to leave him alone, then walked/carried him home (1.5 fucking miles!!) while she stormed off ahead and offered zero assistance.
I'll speak to DP about inviting him out for a beer, either just the two of them or the rest of their group, to give him a little pep talk and see if he wants to open up about things, and that he still has all of our support whatever happens.