What Does This Mean To Me?

The backstory for this post is here.
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It's funny as I read that prior post myself....I see I ended it by saying "I'm not sure what to think about it yet." And here with the latest twist in the story, I'm in the exact same place. I'm not sure what to think about it.
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In fact, I'm not sure I ever really processed the incidents of the prior post on an emotional level. I'm not sure there was anything even there to process? That sounds wrong....I have to think there WAS. In any case.... I called my Mom on Saturday AM to ask her a baking question. I'm a good cook but Mom's my guru! She sounded distracted so I asked her was she busy? "No," she says "your brother spent the night and *waaah*waaah*waaah*waaah*" (Insert sound of Charlie Brown's teacher here because it's all I heard after that)
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Huh?? I managed to gather a couple things in my haze. Something about changing apartments and had nowhere to stay for a night so she had him stay with her. She sounded all bubbly about some changes in his life and I was just silent. "Okay, thanks for the baking advice....talk to you later."
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Now, I was skeptical when she said it was the end of all contact with him before. And I know she's seen him a few times since that all happened. I don't know...this was different. All that talk about everything out of his mouth being BS and he's nothing but a manipulative, pathological liar and now he's a houseguest? I called my friend Jennie after I got off the phone with my Mom...I just wanted to talk it out. Jennie responded with some thoughts about my mother and why she did what she did. Correct thoughts. Hey, I know my Mom better than anyone and it's not hard to figure out why she did it. In fact, I don't really care at the moment. What I'm concerned about it what it means to ME. How do I feel about it?
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In the end, I think I just feel a little confused. I mean, I'd accepted that my mother was never going to see my brother for who and what he was and I was able to move past that and love her for who she was in spite of it. That all happened before her revelation. So why now do I feel like this should change something? Do I feel betrayed? No, I don't. I think maybe it's disappointment? Hmmm...as I sit here with my thoughts, I actually think I feel threatened. I am feeling like I need to protect myself from involvement with my Mom if she's going to be close with my brother again and forget what he really is. Even though I was able to accept her relationship with him before, I think I've let my guard down bit by bit and let her closer to me since her realization about my brother. You'd think I'd be more in touch with the feeling of needing to protect myself....I've lived with it forever.