He is married to someone (not with someone!)

Many students make this mistake because the preposition

'with' makes sense ("he is with her" is correct).

And in many languages, using 'marry' + 'with' is correct!

And there's another confusing thing. When we use the verb

'marry' in the active voice, we don't use any preposition at all:

"I want to marry her" (not 'to her' or 'with her')