I wonder if your rational thinking is getting confused by the prospects of getting some deposit from that person?
He needs, amongst other things :
•online access username
•online access password
Ok, so you have 1000 in your account. They deposit 500 and you are happy. Then they take out all 1500 and you're done :) How can you not think it is a scam when you're giving them your login as well.
Here is an analogy. Some stranger asks you for keys of your home (while you're away) and tells you he will just go in place a gift inside your door and go away. Would you give him your keys and come home later expecting a gift to be there and nothing taken away?
Is it a scam if the person only wants to deposit into my account, not make a withdrawal?
Who is to tell?
P.S: Sorry, please don't mind the rest of this answer but from it could also be related to a new relationship that you are in. Going ahead with this might cause you a lot of emotional harm as well. You seemingly trust that person when there are obvious signs that you are being defrauded, possibly in the name of love.