Breakdown of Est-ce que tu lui mens souvent ?
tu
you (informal singular)
souvent
often
lui
him / to him / to her (indirect object)
est-ce que
is it that / do / does (question marker)
Questions & Answers about Est-ce que tu lui mens souvent ?
Why do we use lui here instead of a direct object pronoun like le?
Does lui mean "to him" or "to her" in this sentence?
It can mean either one! As an indirect object pronoun, lui is used for both masculine and feminine people. Depending on the conversation's context, this sentence could just as easily mean "Do you often lie to her?".
Why is lui placed before the verb mens?
What verb is mens from, and is it a regular -ir verb?
It comes from mentir (to lie). It is an irregular -ir verb. Similar to dormir (to sleep) or partir (to leave), it drops the "t" in its singular present tense forms: je mens, tu mens, il ment.