I don't think you've been dishonest at all throughout this process.  You seem like a good guy that always tries to find the good in people.  This is a great characteristic in life, but it seems pretty clear that GP took advantage of you being a nice guy.  I'd be surprised if he put much effort at all into returning Jennis money.  He got her to ask you to send him money because he's a scammer, not because he tries to help people.  If he was actually in the business of helping people, there would be more than 1 person after 3+ years confirming that he actually helped them.

I hope you understand the reason everyone is giving him shit and ruining his reputation isn't just to be mean to someone.  It's to make it harder for him to scam people in the future.