I don’t think that your suspicions are unfounded. She likes this other guy and he likes her. It’s understandable that you’re jealous, and I would never label you a fool. You can’t control her, and if she likes someone else and you no longer feel special around her, it may be time to consider that you have some competition!
That said, I don’t think that your idea of bringing this up is a good one. Having a talk about your jealousy is going to create the problems you think it will. It’s a much better idea to try and win her over, rather than either make her stop seeing this guy or trying to control her feelings.
I’ve written a book for men who want to win with women called Date Out of Your League, and you can buy and read it here: [url]https://www.askapril.com/relationship-dating-advice/date-out-of-your-league.html[/url]. You may get some good ideas on how to continue to win her affections back.
I hope that helps. Let me know how things go, and follow me @AskAprilcom on Twitter and on Facebook at this link: [url][/url].