I dated this guy, and he disappeared... he finally resurfaced a long while later and I basically told him not to contact me again. He hasn't and now I feel like I ruined everything and want his attention again. How so I do this?
Well, why would want a guy back who has disappeared once before? I mean he did it once and broke your trust so there is every chance he can do it again.
However if you are absolutely sure you want to be with him, then contact him, arrange a meeting and have a discussion with him, ask him to assure you that he will not disappear again. If he gives you an assurance then you may have a chance of being with him again.