Complex sentence: After moving to Tokyo together Izumiko and Miyuki grow closer, but Miyuki doesn't believe he can truly protect Izumiko since he is weak and can't even take care of himself.
Split into simpler sentences: After moving to Tokyo together, Izumiko and Miyuki grow closer; but Miyuki doesn't believe he can truly protect Izumiko. He believes he is weak and can't even take care of himself.