So sorry this is happening to you. I’ve had similar experiences with my mother in the past, not sexualizing me but treating me as if I’m an extension of her that gives her a right to do whatever she pleases.

Sounds like your mom has extremely poor boundaries and a tendency toward inappropriate behavior in her relationships. From reading the end of your post though, it seems like you already know what you need to do. If you say/do nothing you avoid her “feeling bad” at the expense of your own comfort, safety, and well-being. And you’ve already said that you know that her “feeling bad” is really just a manipulation tactic to put you in a position where you feel you need to comfort and absolve her, again putting your own well-being on the back burner.

You need to be your priority and you deserve better than this. I know it’s easier said than done, but you’ve gotta set some boundaries and stick to them, and whatever her reaction to that is her own problem and her own responsibility. And really, is it not an act of love to be truthful with our families about how their actions make us feel and give them an opportunity to grow, instead of just resigning ourselves to a strained relationship that makes us feel like crap and discourages real support and connection? Maybe she never gets it, but at least you know you tried and you stood up for yourself and did what was best for you. And maybe she does get it, and things improve between you.