Here's a little more legal advice (actually it's business advice).

If you don't have a company established around this invention, you don't have much of a legal framework to make a claim on it. The idea predated your meeting the inventor. I doubt you have anything in writing that says, "You set up a website for me and I'll share royalties with you." The value of the invention is purely speculative since no money has been made, not contracts have been signed.

Keep in mind that it is fundamentally in your lawyer's interest to give you undue hope. If you're paying him hourly, he's being paid for fighting, not for winning. To get a real sense for the viability of this, ask your lawyer if he'll accept a cut of the royalties you hope to collect instead of his hourly rate.