Liking my best friend

I met my best friend, let’s call him Jack in October last year. We were friends immediately and became best friends in February. I realized I liked him more than a friend while we were at a dance alone in March. Near the end of the school year I thought I’d tell him my feelings because if (what I thought was the worst case scenario) it weirded him out we wouldn’t have to face each other. It went worse than I thought but in an unexpected way. He told me he liked a girl, let’s call her Dorothy. Obviously it hurt a lot, even more so when I realized he barely knew her and I had basically spilled everything about myself to him. I decided to not say anything to avoid ruining everything. However now that he told someone he trusts he won’t shut up about her. 24/7 he’s only talking about how pretty she is and how much he likes her. And recently he’s starting to talk to me less as he’d rather be texting or hanging out with her. I’m happy for him, but at the same time it’s getting so painful to where I can’t look at him or be in the same room as him. My family and my friends have told me that I’m more closed off, so I’m considering risking it all and telling him. But at the same time I know he trusts me, we rely on each other and I’d feel like I was betraying him in some way. What do I do?