Maybe we do have a habit of letting our mother push us around too much. I have no clue. But on the issue of separate rooms, there's not much you can do, and you don't have much of a leg to stand on. My lady and I were traveling to her mother's home for thanksgiving, and since Mama pays the mortgage, she gets to create whatever rules she sees fit for her house. It's a dictatorship, not a democracy.
And this rule, about unmarried adults not sharing a room, is pretty common for some households. I'm sure there's at least one set of random parents who are like, "Sure! Sleep together!" but I haven't met them or heard of them yet.
The stories I do hear illustrate what extremes many families take with this rule. For instance, after reading a query, I joked with my friends mother that my Lady and I should be able to share a room the next Thanksgiving, since, you know, we might get married. Her response: "Was there a wedding ceremony that I didn't attend?" Bottom line: "put a ring on it and say your I do(s)" this isn't good enough to share a bed in her home; only a marriage license grants permission.
I mentioned this story to a friend, who responded with a story about how her mother once told her own 60-something brother who was visiting with his live-in girlfriend that they had to sleep in separate rooms. Being an unquestionably grown man and all, who wanted to sleep next to his woman, he wasn't happy about that. But it was either abide by his sister's rules for her home, or don't visit and pay for a hotel. He went with his sister's rules.
I realize the "separate beds" rule was "a black thing" when I taped a relationship-panel segment from VH1... and plaid it back for some friends. The hostess asked whether sex in your parents' house was a "yea or nay," I was sitting with some friends and said "I thought all families, of all colors, operated that way." Everyone else was sort of shocked. "You can't sleep in the bed with your boyfriend when you visit your parents?!" They looked at me just as crazy as I was looking at them.
My friends came from more liberal households, possibly like some of my nonblack friends from college whose parents thought nothing of them dating at 12, having opposite-sex sleepovers in high school or their boyfriends sharing the bed when they went home together on school breaks. That's not better or worse than how your mom operates, just different.
I explain to my girlfriend then that her mom had a more conservative outlook, my mother always had that outlook, and that the no-sleeping-together rule wasn't personal. I threw out a story about the time when I brought a woman home to my apt. in NY when my mother was visiting and the same rule applied (even though it was my apt). My mother and my mother-in-law and all Black mothers I know saw things the same way. If a woman is really offended by your mother's rule, then there's always the option of doing what my friend's uncle didn't: Don't go, or get a hotel room. By staying put or heading to a hotel, you can sleep however you want and do whatever you want in that bed, without breaking Mama's rules under her roof.