Will my boyfriend's mom really start treating me better after we become engaged/married?

so, here's the deal. ive been dating my boyfriend for about two and a half years, and almost everything is perfect. the one main problem we have is his mom and the way she acts towards me. every boyfriend i've had in the past, their moms LOVED me. invited me on trips, to dinner, family gatherings, etc. and just generally looked happy to see me. SHE can barely be bothered to say hello to me. i am uninvited by her to things my boyfriend has already invited me to, by her saying its "family only". obviously, this is extremely hurtful and upsetting to me, considering he is warmly embraced by my entire family. i can honestly say that this woman and i have never had any type of problem aside from the ones she created by being cold towards me. i have never even gotten into a fight with her after she does these things, for my boyfriend's sake. he has evern tried to talk to her and tell her she hurts me when she does whatever but she pretends she has no idea what hes talking about, so theres really no way for a discusiion to take place. my boyfriend says that right now, she just thinks of me as another girlfriend and that our relationship will eventually run its course so she doesnt really have to bother to get to know me. my boyfriend says that once we are engaged shell realize were serious and basically he says a switch will be flipped and theyll all you know be my best friends. i find this extremely hard to believe. i am worried that she will always resent me for taking her "baby" away. she is extremely dependent on my boyfriend and i feel she tries to use him as her own boyfriend since she has been divorced. she always wears his t shirts and wants to sit next to him on the couch and watch movies and hold his hand (hes 21). frankly, its just weird. she always wants him to come home on valentines day (without me of course) which he never does, but then she guilts him about it. she is just so obviously disrespectful of the love we have for each other. i am a good girlfirend, ive never cheated or caused any great rifts. i dont understand how a grown woman could be so immature. if i try to initiate conversation when we are alone she literally will say nothing back, and its extremely awkward. i dont want it to be like this forever, so i hold out hope that my boyfriend is right and eventually they will be nice to me. but the logic inside me says that this will never change. i guess what im trying to find out is if anyone has had an experience like this which ended up working out all right, or if this is just a recipe for disaster. i guess i should add that since i have expressed my feelings on this, he has really made an effort to change his moms behavior and to do everything he can to make me feel more comfortable around her. i still feel he sometimes bends to her demands too much, but he really has made a noticeable change in the way he acts toward her (he used to do everything the woman said, no questions asked). this is my first time posting a question so i hope i gave all the necessary info, thanks everyone!