It sounds like you're now considering not marrying him, which in my opinion is 100% the right thing to do.
I saw a friend get married to a very abusive man last year and she is now divorcing him. From before they were married they were arguing constantly, he was always calling her a 'money grabbing bitch' and doing horrific things, however then he would apologise and unfortunately, she seemed to think that once they were married things would change - and they did.... for the worse as she couldn't leave him so easily and admitted on a number of occasions that if they weren't married, she would leave him - However as they were married, she felt she should 'try' to save their marriage, which actually was her bending over backwards to try and change everything about herself and him behaving incredibly badly.
Just before this friend got married, I mentioned my concerns to a work colleague (also a friend) and my work colleague said her marriage had lasted 6 WEEKS and that she found out that her husband had actually been having an affair for the previous 6 months and when she confronted him 6 weeks after the wedding, he had physically assaulted her so badly the police were involved and she's got permanent injuries.
I'm not suggesting your fiance is anything like these 2 men, however, one thing my work colleague said to me was:
^"Fluffy, I wish I had had a friend who had said to me that it was OK to cancel the wedding.....
....When I mentioned to my friends and family about cancelling, they said I just had 'cold feet' and I felt I had to go through with it as I didn't want to disappoint them. Looking back, I should have listened to my gut..... Please be that friend for your friend and try and say to her, she doesn't have to marry him, there is always another option"^
So, I tried.... 2 weeks before my friend got married, I phoned her up and told her, she didn't have to go through with it, there was always a bed at our house if she needed it - she had options and it was totally up to her.
Unfortunately, she did go through with it, but I'm glad I tried to at least show her that she didn't have to marry him (which she now admits was the wrong decision).
OP - Maybe think of Mumsnet posters as those friends? Ultimately, it's completely your choice, but I'd suggest not ignoring these doubts or putting them down to 'cold feet' as it doesn't sound like this is what you're feeling. Regardless of the pain and cost of cancelling a wedding, it's far, far easier to do that, than to divorce.