No I don't think it's possible to love someone too much.
It's almost like saying is it possible to be too happy.
Having said that there are various types of love.
A parent may be willing to give their life in order to save their child. Would one consider that loving too much?
A man may sacrafice his life to protect his wife and family from an intruder....Would you say he loved them too much?
Now when it comes to dating: A person may wonder if they are "loving someone too much" if they realize they are not getting back the same type of love. I do believe it is possible to love and adore someone more than they love and adore you. Staying in that type of relationship begs the question "Why don't you love (yourself )enough to find someone who is willing to put as much into the relationship as you are?" It's unhealthy to be in a relationship where one person does most of the giving and the other does most of the taking.
Allowing yourself to be used is not proof that you love someone too much. It's proof that you don't love YOURSELF enough!