Stand your ground, if he likes you he’ll change his mind about the open relationship part. If he doesn’t like you enough to reconsider than trust me you don’t need him. It feels so awesome to be really love by someone. Someone will come along who wants you and only you. That’s the guy you really want.
A lot of women that I’ve met don’t feel comfortable being just friends with men. They think it’s weird and awkward. I personally have always had a lot of male friends. But I’m not usually single and I think that makes a difference. If your single that changes the dynamic a bit.
It might be a situation where you do something different and keep the friendship going and try to stretch yourself as a person and if you do that think of all the single men he may introduce you to when you go out and do friend stuff together. You might meet someone really interesting.
good, I’m personally really glad you are planning on remaining friends with this young man. If you like someone that much they surely have value as a friend.
I think mentioning open relationships is a really big red flag. Assuming you can change them is also bad. I’m not saying you are doing that, but guys who are serious about a relationship with one person don’t mention open relationships, they focus on you and give you their full attention.