Do Not Wear That Mantle of Shame
When we get "used" by someone, we feel the shame.
That's messed up.
Think about it. If you got used by someone (whether it's in love or business), you are not the one with questionable values. If you did as well as you could in whatever this relationship was, if you worked with a good and honest heart to the best of your abilities, then you have nothing to hang your head about. (And if you didn't work with a good and honest heart to the best of your abilities, then you need to ask yourself some serious questions.) But, if you have no actions that caused whispering, kick shame to the curb and march on.
Don't beat yourself up with "I should have known better." Shoulds don't help. You can't rewind and undo. But you can learn and heal.
The user is the one who should have some trepidation for their future. It might look bright now, but the universe is a patient schoolmarm. She gives the lesson when it will have the most impact. In the meantime, pick up your head and your heart and forge onward.
The world is big. Go find your new adventure and throw your heart on the line again. That's what the brave people do.