I totally get where you're coming from feeling a little weird about this situation, but based on the facts-- you acted professionally, the property wasn't a good fit for you (and the numbers weren't working for you which is totally FINE even if you were being extra conservative- that's YOUR prerogative). Then, when you stated you didn't want to purchase it for $91k, your PM said he was going to buy it but he usually only pays 50k for "these types of properties". Ummmm... some mentor! If he would only pay 50K for it, he should be advising you of the same. If he was wholesaling the deal, as @Nicholas Scatton suggests, then he should have been transparent about that (and I agree with Nicholas- I think he was)
Don't be made to feel like you did anything wrong- you just avoided a bad deal! (It might not be a bad deal at the price of $50k though!) Just because you're a new investor, doesn't mean you can't know your numbers and your market.
Furthermore, I wouldn't necessarily cut ties with this PM, but I would pay close attention to the work he's doing for you- he's shown that he lacks integrity and may take advantage of you in other ways. Also, you can breezily say/text/email- "sorry this one wasn't a good fit for me, but feel free to send me any other deals you may have- I'm open to more properties in this area". He may not send you more, but it's ok for you to remind him you're still looking. Plus, as your PM, he knows the more property you have, the more business he has.