I just started a conversation about pan-romantic, non-sexual open relationships with a good friend who I know used to be interested in me romantically. I’m not interested in him as more than a good friend but he’s a really open-minded guy and it just came up. I want to continue talking to him about poly and asexual relationships, not because I want one with him but because it’s something he seemed interested in when I brought it up. How do I do this without ‘leading him on’?

First off, good on you for being so in tune to another person’s feelings. It can be humiliating to believe that someone is interested in you only to find out you were misreading signals from their side. 

As in almost all situations, clear and honest communication is the best answer here. If he knows that you know he used to be interested in you romantically, I’d recommend just bringing it up, acknowledging that it’s sort of awkward. Something like, “I just want to say that I love talking about this stuff with you, and I really appreciate how open minded and insightful you are - I just wanted to check in and make sure this topic of conversation is comfortable for you, considering our history, and that this is all entirely platonic.”

Either he laughs it off like no, that’s not a concern, we can chat like friends; or he says actually yeah, if you’re not trying to signal romantic interest then this isn’t something I prefer to talk about with you. In both those situations, you can smile and say you just wanted to check in! Don’t make it out like a huge serious talk, or that you’re implying that he’s some lovestruck unrequited admirer. Just a friendly check-in with a friend. Good luck!