Hear me out: Savage Raph as a metaphor for repressed anger.
Because it's like: Raph spent so much of his life knowing that he could hurt someone if he got angry, that he had to restrain himself even in the most emotional moments, or he could be a danger to his own brothers. He couldn't let himself fully express his anger, not until he was alone.
Then the whole hero thing got started, and Raph started to build up a moral code. We see through the whole movie that he takes the hero role very seriously, putting in all his effort to protect others. Again, Raph couldn't let his anger win over, because it would go against his one goal of keeping others safe. Again, he couldn't let himself express his anger until he was alone.
But then, the instant Raph is alone, the instant he doesn't have to worry about hurting others, there's nothing to stop all that anger from bubbling up, from overwhelming all of Raph's other emotions all at once. Then, once the anger has got the best of him, that's when Savage Raph able to turn on his brothers; after he already got to his most emotional point.
Just. Savage Raph being something that goes against all of Raph's values. Anger being something that goes against Raph's values. All that anger building up over time, until it all boils over, during the only times when Raph isn't faced with the overwhelming fear of hurting someone else- the times when there's no one around for Raph to hurt.
Raph hates this of course. Savage Raph goes against everything Raph tries to be. And by extension, Raph starts to hate being alone too. He starts gettting anxious when he's by himself in the lair. Raph needs to be around someone at all times, because if he is ever really alone, he will lose control of his emotions; and for Raph, that's the same thing as losing control of himself.
















