ChocoChoco:

Reading your post you obviously have a lot to offer–smart, educated, resourceful, job, organizer.   My thoughts are slightly different from Anita’s–confirm you are comfortable with this MIL arrangement or find boundaries for yourself before you get married.  Simply put  I have walked a similar path.

Your dear fiance has an understanding with his mother that goes back years before you arrived on the seen.  He takes care of her, bends to her wishes and she does not have to behave like a responsible mature adult.  For whatever reason, they are bonded and that works for them.  Consider the possibility that you may be a welcomed party because you multiple his ability to give to his mother. You joined in their dance and everything will be fine if you continue doing their dance.  But if you don’t, what will happen?  This is the answer you need to find out before you marry him.  The following are a list of questions, I wish someone had raised with me:

Are you loved for just for  being a loving  and kind person or for what you can do for the fiance and his family?

Does your fiance see you as first in his life now and building a life with you (with his mother second)?  Or is he always trying to fit her into your plans with him or squeeze in calls or visits to see her (particularly during a time that is supposed to be reserved for you) because she needs something or is upset?

Is your fiance willing to set boundaries with his mother to protect what is important to you? (Asking him a billion times or explaining over and over why this is important with him quietly nodding does not count as a yes.)

Will you have enough energy in the future to raise/develop your kids (possibly work outside the home at the same time) and cater to your MIL?

Realistically, since she has little to no resources, have you thought about the real possibility she may ask if she can move in with you and your fiance someday?

Personally Choco Choco, I think your intuition that motivated you to post is spot on.

If you decide you definitely want to marry your fiance, my suggestion is to set boundaries for yourself.  With kindness and love, limit how much help will personally come from you.   If she comes over, find some place else to be. Let your husband be responsible for entertaining her and meeting her unreasonable demands.  With regard to money, have 3 accounts (his, yours, household) or he is on an allowance.  If he wants to spend his whole allowance on her that is his choice.  But her needs do not come before the financial needs of your household and future kids.

My MIL was sweet but a TON of work and could never stop talking and a HUGE snoop.  She was sooooo much work for me when she visited–I cooked, cleaned and listened to her for hours. Meanwhile my husband would sleep or go watch tv.  When I complained he told me I was not like him–family oriented.   After years, I met someone who gave me the advice I am now giving you.  When she was coming, I reminded my husband to go food shopping, clean the guest bathroom, guest room. I encouraged them to go to the movies or just excused myself.  Guess what?  Before you know it he was complaining she was coming over too much. LOL.

Listen to your inner voice.