I love you but I can't be with you, what does it mean?

Since I have been on the subject of love, I do not get what it means when some one says I love you, I will always love you, I am deeply in love with you and always will be… but I can’t be with you. What does it mean? Is this something that players do? I know love is more complicated than it seems but I think when some one uses this line they don’t love you, and it is wrong to use such a strong word. What are your thoughts on the matter?