Learn Dutch: Ben jij verliefd op haar? - Are you in love with her?

This is a fixed combination. In Dutch, you don't say you are in love with someone (met), but rather that you are in love on someone (verliefd op). You just have to memorize op as a set pair with verliefd.

Why is the verb ben missing its "t"? Shouldn't it be bent jij?

When the pronoun jij or je comes directly after the verb, you drop the -t ending. Since this is a question, the verb and subject swap places, triggering this rule. So jij bent becomes ben jij.

Does using jij instead of je change the meaning?

It changes the emphasis. Jij is the stressed form of je. Using it here makes the question more pointed, like asking "Are you in love with her?" If you just wanted to ask casually, Ben je verliefd op haar? would be the standard way to say it.

Where does the word verliefd come from?

It is built from the root word lief (sweet or dear) or liefde (love). Adding ver- to the front and -d to the end is a common way in Dutch to turn a noun into an adjective describing a state of being.