Complex sentence: Ishida started to ignore those around him (imagining them with a large X across their face) and was driven to the point of suicide, however, he changes his mind after he apologizes to Nishimiya and begins to spend time with her.
Split into simpler sentences: Ishida started to ignore those around him (imagining them with a large X across their face) and was driven to the point of suicide. However, he changes his mind after he apologizes to Nishimiya and begins to spend time with her.