Struggling to date multiple people at once

(26F) I don't understand why I can't go on dates with multiple people at once. I try to keep my options open, but whenever I go on dates with other guys, I can't stop thinking about that only one person I really like. He suggested that I should try dating multiple people (after I told him I did not think that I want to go on dates with others), and I still gave it a shot because I wanted to see what the experience would be like, especially since I haven't been single for 8 years. I've realized that with the guys I'm not interested in, I don't care about their opinions or validation. Whether they like me or not doesn't matter to me. However, with the guy I really like, I find myself automatically being exclusive to him, even if he hasn't asked me to be. I seek validation from him and him only. What's wrong with me? Isn't it the norm of the dating culture?