You are a person with emotions. You reacted to something that happened to you. You are not perfect só your reaction maybe wasnt the best. Its ok.

You cant just go from having a romantic relation with a person, to seeing them date with other people the next day. Hell, it can even hurt years after. We dont control what we feel, all we do is learn how to deal with them. You're are still young.

IMO this is not a FU.

You will be alright.

Also, that guy wanted you to know he was dating. Trust me.