I felt sad after I saw my crush talking to my enemy?

So today I had a netball practice. Then I had a recess and I saw them talking romantically on the school field. I just felt so angry and jealous. I know they're pretty close and I know I shouldn't have felt like that because he's not mine, but I really love him, and plus, he's talking to someone who I really don't like. Then when I got back into the practice, I couldn't concentrate because I was just disappointed and distracted. My coach kept scolding me because I kept making mistake. Now I got home and I just felt so freaking sad. What do you think? Am I overacting? What should I do? Please no rude answers, thank you.