Love is an umbrella term for a variety of often conflicting concepts, I think. Unconditional love can't ever bring anything but positive, joyful states of being.
But if you "love" with the desire to receive emotional sustenance from someone else, if you're needing something from them, then yes, the ultimate conclusion to the relationship will inevitably be disappointment and pain. It's just not possible for your heart to be "fed" by someone else for in a continued, sustainable, and real way. *You* have to do that for yourself.