Being an "idea person" is not comparable to being an "implementer." Truly exceptional individuals can be both, but I'm willing to wager that this whole venture was OP's idea, thus making him the "one true founder."
Diplomacy would be best for OP, but they shouldn't close the door on exploring their legal options. Especially if they have anything dated or timestamped that clearly establishes them as the originator of the idea or concept.
All in all, this is a valuable lesson for OP and they will walk away from the experience with wisdom to help them in their future ventures. Best of luck, OP.