Responses
He did propose off screen that's why we see them wearing it in the next chapter. And yep, the first one was for proposal only, engagement rings are usually chosen by one of the pair usually the one proposing and wedding rings are chosen by both people that's why Koutarou asked Tsuguya to choose with him and brought up registering their marriage as well.
Why did he not enz up wearing the ring A originally bought for Y. They went and got another pair of rings instead, was the first one only meant for proposal? But he aint even propose w it