Your young and I think it's perfectly fine for you to experiment with whatever you and a partner chooses to try. Also, I personally don't think there is anything wrong with cock worship. That's primarily what this site is about anyways.
At nineteen, you're just out of the schoolroom literally and how will you learn things if you don't experiment?
Porn sites like this often offer a Classified section. Think carefully on what you want to communicate to the type of person you are looking for along with a few pics. If you don't post pics, doubt you'll get much of a reply.
Besides lpsg, try xhamster, xtube...can't think of any other good places right now. Plentyoffish or okcupid - no porn pics allowed, but popular dating sites.
Have fun. And please take condoms and use them. It would really suck for you to get aids or another disease. It only takes one time. Also... Please be honorable and show your gf the respect she deserves by telling her you want to try this. If you cheat on someone now, you'll most likely remain that way.