Complex sentence: Green's reaction to Lupo is somewhat reserved at first, especially since the first case they work together is Lupo's brother's suicide; however, after a short period of time, Green seems to become more comfortable with Lupo.
Split into simpler sentences: Green's reaction to Lupo is somewhat reserved at first, especially since the first case they work together is Lupo's brother's suicide. However, after a short period of time, Green seems to become more comfortable with Lupo.