Complex sentence: Barnabas, on his part, wishes even more desperately to be mortal again, but finds out Julia is just using his blood to make herself immortal, so he kills her and dumps her body into the bay with Willie's help.
Split into simpler sentences: Barnabas, on his part, wishes even more desperately to be mortal again. Barnabus finds out Julia is just using his blood to make herself immortal, so he kills her and dumps her body into the bay with Willie's help.