What can I do about my guy friend ?

My guy friend I’ve known for 2 years is getting married to a girl nobody can stand ! she is SOO rude to him it’s not even funny , she steals money from him , she ignores him to talk to her ex , she’s called me and my friends fools , she just doesn’t give him the love and respect he deserves , he doesn’t like her either , they’ve broken up a few times , but got back together he thinks if he doesn’t marry her no one else will , he just wants to get marriage over with , I really care about him and actually want him to be happy , I was talking to one of my friends , she said I should just let him marry her , realize he made a mistake and let him be miserable , but I can’t and won’t stand by and let him be like that , so I talked to my other friend , I told her “ face it , he’d be better off with me than her “ well my friend said that was probably the only way to help him , I thought about it , I would so date him and marry him just to make him happy I care about him that much , but this is a HUGE decision I can’t make on my own , so should I let him marry his friend , or should I step in ? I don’t want to see him unhappy , and how can I tell him I’d date him and marry him ? and please don’t tell me to think this through , I need a decision ASAP thank you all so much