Quote Originally Posted by basurero
I would like to tell you that my original sentance DOES make sense.

"I saw the man which is with the girl."

As in the man who is with the girl RIGHT NOW.
Err no, it doesn't. At all.

"I saw the man who is with the girl."

or even

"I saw the man that is/ that's with the girl."

You categorically cannot use 'which' here (and you don't need to use 'with whom' in this case either)