Complex sentence: Clark, unable to reveal to Lois that his mild-mannered demeanor was a ruse, was unable to compete for Lois' affection, the irony being he was his own rival seeing that Clark and Superman are the same person.
Split into simpler sentences: Clark, unable to reveal to Lois that his mild-mannered demeanor was a ruse, was unable to compete for Lois' affection. The irony being he was his own rival, seeing that Clark and Superman are the same person.