Complex sentence: Garrity is thinking about telling Tommy that he is dating his sister, asking Franco what he thinks, Franco runs away from him; telling Sean that he doesn't even want to be involved, that way he isn't a victim of crazed retribution.
Split into simpler sentences: Garrity is thinking about telling Tommy that he is dating his sister. When he asks Franco what he thinks, Franco runs away from him; telling Sean that he doesn't even want to be involved in the discussion, that way he isn't a victim of crazed retribution.