*pat pat*
I don't know if I've said this before, but if you're confused about who and whom, try replacing it with he/him or they/them. This often involves rearranging the sentence or answering the question or something like that.
For example:
Who did you give it to? I gave it to him.
So it should technically be "whom," not "who." But if you can't figure it out and have to use one, always go with "who." Yes, it might technically be wrong at times, but at least everyone does it. If you use "whom" when it should be "who," then you'll really look ignorant.
Oh, and nobody worries about ending sentences with prepositions anymore.