My stbx husband was and is a mommas boy. It doesn't change. My stbx is still controlled by his momma and so is all of his brothers. She has damaged him emotionally and I blame her for a lot of his bad qualities.
Good luck with things changing after the marriage.
I think it's ok to always be willing to help our mothers with certain things they might need. But when they ALWAYS need something and you can't say no like your future husband, it does become a problem. He doesn't complain or say no because like you said, he doesn't want to have hell break loose at the house for his brothers. Having respect for a mother is one thing, but not standing up to her or not being able to say no is another. He shouldn't feel obligated to do anything. If it gets her that upset if he says no, you know there's a problem and so does he or he wouldn't be scared to say no, right? Having one of those mother -in-laws myself that doesn't respect me and is controlling, I understand you. But like others have told you in this post, think about it because if he's like that now, it'll be a miracle if he changes just because you're married. I have been married for 4 years and my husband still has trouble standing up to her when it is necessary. Don't feel guilty because her behavior bothers you. You're entitled to get upset if she is the way you say she is, but you must remain respectful to her and let your husband handle her. That way they won't have anything to hold against you. Talk to him about it to make sure he agrees with your point of view. Everyone has a breaking point though and if you feel that you will reach yours soon, just avoid being around her by yourself.
If you have a son with him I hope he will teach his son to respect you as much as he respects his own mother. I think it is sweet what he does for the woman who gave him life.
Does he complain, or is it just you?
I have a sneaking suspicion that you will be the one who will be upset the rest of your life. And not just until his mother dies. This is about him. Like RR said, don't bank on marriage changing anything significant for the better. People are normally on their best behavior BEFORE marriage--not the other way around. What you are seeing is what you will be getting.
You shouldn't have to work so hard and look to the future for things to be better. That is honestly not how it's supposed to be. But I do know from the many posts you have posted about various issues that any advice you get from those who have been around a while falls on deaf ears. But that's ok. It's out there nonetheless. Consider it--or not.
I do wish you the best, too, though.