You have to take a step back and let them get on with their life without you. You have to let them go so that they can eventually let go of you. Neither of you will be able to get on with your (love) lives until he/she has moved on.
Any contact will lead them on. First take Christin's advice, but then walk away (let them know you're doing it and why you have to).
There've been a few men in my life who I've had to leave behind because although I've loved them as friends, I haven't felt the same way as they have about me.
If he/she truly loves you then he/she'll let you go. and if you care about them you'll help them to do that.