I need advice. should I reach out?

there's this guy who saw me last year at a race. he friended me on Instagram and messaged me saying he thought I was so pretty. I never followed him back. We talked for two days. The one day he told me he had homework and had to go. We never texted after that but every time he sees me he says hi. The other day I freided him back on Instagram. He looks single. the only thing is there's a post of him and my ex together.

Do you think he stopped texting me because he lost interest or do you think my ex said something?

Should I reach out and say hey and start a convo about the race or just leave it and when I see him at the race say something? Also if I see him what should I say?

Updates
+1 y
I saw him and said hey I think it went well. I'll explain so I walked past him and we smiled at each other. Then I texted him and said good luck today. He said thanks you too. Then I saw him again and we talked a bit. Every time he saw me he would look over and smile even if he back was turned to me or he was with his friends

The only think is we texted a bit and it's always me asking questions. He always responds right away but he hasn't responded since last night. How do I interpret everythin
I need advice. should I reach out?
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