Help with Expense Report

What I am trying to do seems pretty simple, but as I never use Excel I am not sure how to do it.
I am trying to create an Expense Report for me and my partner.

I have two columns that are of interest. One Column is the Amount paid for an item and the other is who it was paid by. As we are just entering this information as we add on the the expenses I would like to separate the amounts paid by each person to compare who owes who and how much.

So if a cell in the "Paid by" column has my name, then it should take the value from the cell next to it and add it to a sum. Hope that makes sense.

Thanks