Alright, Ill try to break this down for ya.
Spike left the Bebop to fight the syndicate for a number of reasons. A lot of which is hypothesis and what not because its left for interpretation, But, he left because he wanted to protect Jet and Faye. You see in the previous session that they ship got attacked by the syndicate and that Jet got shot in the bar. Spike realized that by stayin with them, he is endangering their lives. You see in that session how much they focus on Jet's wound and Spike focusing on it. This is unlike all the previous sessions where we see the members suffer much more serious injuries. He also left it obviously for revenge for the death of Julia. Then theres the whole angle where people think from session for 5 (Where spike falls from the window, and people believe he dies) or Toys in the Attic (where some people believe all the members died) that the rest of the series is Spike's dream. Hence why he says "Going to find out if im really alive" and Julia says "its all just a dream"..I personally dont believe the latter but thats up to how the indiviual interprets the show. What makes bebop great!
The Youre Gonna Carry Your own weight last text is symbolic of the relationships of people. Youre gonna have to look that one up yourself because its far too much for me to type at the moment (doing this post quickly).
Ed left to go stay with her father and for other abstract reasons.
Hope that clears some it up for ya lol. If you have any more questions, just let me know
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