TL;DR: OP's best plate doesn't shit-test and it's anomolous.

Backstory- I started hanging around a guy I work with and we became pretty good friends. His sister was around often, so I offered to take her out. She's my age (early 40's), in shape, responsible, and attractive. After clearing it with her brother that it would NOT cause a problem between he and I, she called me and asked if my offer still stood. I took her for a stroll in the hipster part of town sampling food trucks (keep it under $40, fellas) and she confessed that she always found me attractive and liked that I didn't hit on her like her brother's other friends. (DGAF) After a few dates and some great sex, we went exclusive. It was promising.

She fucks up & gets plated- We went out to see a pretty popular band at a local club. There were some people she knew there. There were some I knew, too. Our crowds mingled together and we were the power-couple of the room. As the night went on, she got increasingly drunk. I tried to reign her in, but it got out of control. She was falling into people, being obnoxious, and I simply got tired of keeping an eye on her. I left her there. DONE. I started dating other women and we would still cross paths since I obviously still work with her younger brother. I kept it polite and peaceful with her. Eventually, I was out alone and we crossed paths again. We made conversation and she ended up coming home with me. She's officially a plate.

Our routine- We'll hang out once or twice a month and she'll spend the night. She knows that I go on dates with other women and doesn't talk about it. She seems content and never asks for an LTR. No trouble. Ever. We even do things together with other couples, everyone knowing that I see other women. Even her her brother knows what I do. Her: She doen't date or sleep with anyone else. Our common friends have confirmed this, including her younger brother. I'm her sole sexual partner.

A revelation- This morning as she got out of bed, put her clothes on, and went home to take her oldest kid to a sporting event, I watched her get dressed and she looked over her shoulder and smiled at me. It hit me right then that she has never shit-tested me once. NOT A SINGLE TIME SINCE I PLATED HER. I've never heard of such a thing.

Only my TRP brothers would even understand what I'm talking about. What gives? Why is she different? Is she dotting her I's and crossing her T's so I'll go LTR? Is she just afraid to upset the apple cart? Opinions?