yes when you cling too much to the person and do everything for her without thinking clearly of yourself
Yes. It's called smothering and it's selfish.
I'm not sure you acting like a douche once in a while would solve the problem of loving someone too much, but rather affect how much they love you... but yes, it's possible to love somebody too much.
too much love is not love...
People can be obsessive in everything .. including "love". When it's an obsession .. it's probably not love at all.