Mom and BF Relationship
TL:DR at bottom
I'm very close with my mom, and I always have been.
I am 26; I still live at home, though I pay rent to my parents and cover all of my own expenses. Because of my relationship with my father, I did not date (not trusting myself not to complete the cycle). I think my mom and younger brother (21) genuinely believed I would stay single and close by forever. Now, that's not the case, and if everything goes as planned, I'll be married this year.
My mom and little brother were both excited for me when I started dating, however as things became more serious, and we became exclusive, they had a different opinion. My mom doesn't like bf because she says he's too shy and hard to get to know, and my little brother says we moved too fast.
Obviously, the most important thing is that my relationship with my bf is healthy and happy, and my family needs to accept that I'm an adult and happy moving forward in my life. I get that. But I still wish they were nicer to him. They're never outright rude, but little bro will ignore things bf says, not greet him, etc.
My mom is standoffish and closed off towards him, and she gets depressed when I talk about the future. She doesn't want to dance with him at the wedding, and when I mentioned that he's considering e-ring designing with my mom so he chooses something I'll like and it'll still be a surprise, she was uncomfortable with that and how "awkward" it would be to spend time with him.
He is shy, but he came to my mom's birthday celebration, has met all of my family, went to 2/3 of our family Christmas celebrations, has come to the house for game nights, etc. He's made every effort to socialize and get to know my family. Nothing is ever enough. I should have expected this, because my mom was not welcoming of my SIL when she first came around either, but I always figured it was due to some of SIL's controlling tendencies, out of control spending, and some rude actions etc. Now that my SIL has given my mom her first grandchild, she's in the clear with my mom.
I've tried talking to my mom about this, but she acts like it's entirely his fault for being shy and gets defensive about it. She's even had some meltdowns with my aunt, and it's clear that she talks bad about my bf to my aunt and who knows who else in the family.
TL:DR I really want my FH to have a good relationship with my mom. But she's depressed that I'm getting married, and thinks that his family "will steal me and any future grandchildren away." How do I encourage their relationship or help my mom be okay with this?
[(Disclaimer - I was saving to buy a house end of 2016, rather than putting money in moving into an apartment with higher rent, but my bf told me not to buy a house because he wants to get married and he already has a house. Later on we discussed timelines, etc. I have never had any intention of living at home forever.)]