If you make this a big deal, then it will be a big deal.
If he keeps harassing you about it tell him you didn't start a rumor about him, and since you do still like him you obviously wouldn't start such a rumor considering the fact it would only hurt you if it were true. It wont matter a bit to you in a year+ unless you make it a bigger deal than it is. I know it sucks since you still like him, but just try and let it slide by. When people ask, tell them no, and possibly add on what I mentioned above. Also, why do they think you did it? If they think you emailed/texted somebody saying it and it went on from there, you can prove it easily. If they think you told somebody who told somebody else, and so on...then that's friggen ridiculous. How on Earth could they possibly know you're the exact one who first said it? Whatever the excuse is as to why they believe you started it is how you can find a way to prove you didn't. If not, like I said...let it go by and it will. If you stop talking about it and he wont shut up about it then people will get annoyed with him.