What's the best way to break up with someone you're not in a relationship with?

We met on an app. We've been dating long distance for a few weeks. I told him I was only interested in dating with the intention for marriage and children. He said he was too, but he can't be sure of where we stand until we've actually spent some time together in person, so we talked about him coming to visit. Since then he's been dragging his feet about making solid plans. I finally forced him to pin down a date and he's looking into flight costs. Anyway, I just had this epiphany that having him visit will be a disaster. He doesn't want this to be serious because if he did, he would be the one pushing things forward instead of me. I want to call things off but suggest that we remain friends. We have a lot of shared interests, values, and cultural background. What's the best way to do this? I don't want to have some big blowup, and I don't want him to see this as an ultimatum. I've made my decision.