It's possible that this might be some sort of phase, or it could be you have an attraction to younger people. Who really knows? Honestly, I doubt there would be some kind of anti-depressant or any kind of drug that would stop this sudden attraction to this boy. It really just takes will power to stop yourself from engaging in sexual practice with him. If you love this kid, it should be no problem. Love doesn't necessarily require sex.
Also, once you're over 18, you can be a pedophile. There are really no requirements for being labeled a pedophile other than being over 18 and having some sexual desire for children or a child.
You should probably explain to this boy about the repercussions if you two should engage in sexual practice. It could get really bad, especially for yourself.