I genuinely can't decide if Ron:
A) knows about drarry long before they ever became official because Harry's always taking about Draco in his sleep. And he's the biggest drarry shipper because he knows how much Harry loves Draco and how long he's loved him for
Or:
B) was completely oblivious like usual and cannot mentally comprehend their relationship. Constantly sputtering "but it's malfoy" whenever Harry starts swooning over Draco, and taking forever to forgive Draco for how he treated Hermione