When someone shares their opinions with you thats when it's important to really listen. You may not think you were the favorite, perhaps you were not too, however, that is how HE felt and probably still feels about how things were and are. And often what that really means amco is more of how you managed to have a relationship better than he could. And, most likely when your mother began struggling mentally it really triggered him to the point where he just could not handle it and got angry. After all, it was the mental illness he witnessed when he was way too young to have the ability to comprehend it or know what to do about it too. Most likely it frightened him and caused him to feel very unsafe. The only place he felt safe was with the people he lived with who provided him with stability. A comparison would be like finding yourself in a place where people do not speak any english and then you come across someone who does and it genuinely brings you a sense of calm again. Finally someone can understand you and even explain things to you so you don't feel so lost and FEEL is significant in this statement.

There is a saying that really does ring true, "You may not remember exactly what a person says, but you never forget how that person makes you feel". So that said, in the example I gave about suddenly being in an environment where no one can speak your language and you can't understand them and they can't understand you, the one thing you will always remember is how that made you feel. And just as true is always remembering how finally finding someone who does understand you and also these others, is the feeling of great relief.

What you need to come to terms with is that your younger brother may never truely get past his deep feelings and may need to distance and do so with anger. And while he may say you were the favorite, it may not really mean what you feel it means, instead he is saying how you seem to handle things better than him, while you can deal, he just can't because it's much too emotionally stressful for him.

Now, your brother did try to reconnect with you and maybe even with your mother. He even apologized to you too. However, that doesn't mean he doesn't carry some very old and very deep emotional wounds. A lot of these very old emotional wounds happened because of his mother's mental instability. It's only natural that her displaying mental illness again can trigger him and cause him to distance, even completely. And it can seem cold, however, he is protecting this very fragile emotional discomfort he experiences.

The other thing that you are missing is that given that he has a very young child himself, he will be subconsciously affected with memories of himself at that age. This can bring very old traumas to the surface. Sometimes not in an overwhelming ptsd way, but, often a desire to prevent one's own child from the trauma they themselves experienced. Yet, it can be more subconscious than conscious.

At this point what is best is to respect his need for space and distance and try to understand what he says on a different level. HIS life experience is different than yours and he was younger and may have been affected on a deeper level than you.