Complex sentence: However, because of his frequent mood swings and tenuous mental state, Deadpool still often abuses or mistreats him, although Weasel has also displayed an opportunistic streak against his friend on occasions.
Split into simpler sentences: However, because of his frequent mood swings and tenuous mental state, Deadpool still often abuses or mistreats him. Although Weasel has also displayed an opportunistic streak against his friend on occasions.