I agree with
@spandit , your mum lives with you, and as far as she is concerned, that's her normal, everyday life of which you are a part. Thinking about and paying attention to brother/ man friend may actually have a bit of an unsettling effect on her, but which translates to you as feeling unwanted, unimportant and just part of the furniture.
I think you deserve a huge pat on the back, you have made your mum feel so welcome and wanted; your house has become her house. Don't feel left out, let her talk to you about your brother to put her mind at rest.
But don't expect a thank you - ever, take pride in knowing you have given mum contentment.
I'm in the same position as you but further along the road (of resentment, and that's a horrible thing to admit).
My mum has lived with us for almost four year's, is happy and fairly healthy but totally dependent on us. She has deteriorated a lot this past twelve months, so all her personal care falls to me now, showering, changing incontinence pads and pants and the "cleaning up" that goes alongside that. Some, most days now tbh, I just want to scream, my world has become so narrowed, I feel as if I'm is here just to service her needs.
For the first time, I am starting to plan a respite break for mum,but what worries me is I won't want her to come home!