Complex sentence: Wolverine is also in love with Jean Grey, who is Cyclops's girlfriend for most of the series, this and Cyclops's decision to leave Morph and Beast behind following an attack from the Sentinels led to Wolverine feeling a great resentment for the X-Men leader.
Split into simpler sentences: Wolverine is also in love with Jean Grey, who is Cyclops's girlfriend for most of the series. This and Cyclops's decision to leave Morph and Beast behind following an attack from the Sentinels led to Wolverine feeling a great resentment for the X-Men leader.