if i play a spell and my opponent uses riposte. does that card count as played if i have heron on a battlefeild? or does my next card count as my first again? And what if i react ontop of his reaction? its my second card played on the chain. what happens then?

No — a spell countered by Riposte doesn't count as played, so it won't trigger Astral Heron. Triggered abilities like Heron's "When you play your first card each turn" only fire when a card completes resolution; a countered card never does (Rule 419.4.a.1, 425.1.b).

If you then play a Reaction on top of Riposte, that card resolves first — it becomes your first card played that turn, not your second, because your original spell is still on the chain and gets countered afterward. So Heron triggers on your Reaction, and your next card after it gets the [2][A][A] discount.

One caveat: countered cards do still satisfy static checks like Legion (those look at Finalized cards), but triggers like Astral Heron require actual resolution.