[There are no shoulds, but he wasn't expecting that. It's still not his worst fear, which was that she would notice that he liked kissing her and be upset with him. So... win?]
Not stupid, not when you have been waiting this long. [Chekov likes Reid, and he doesn't know all of the details of their separation. Maybe Reid wasn't as foolish as he thought and neither of them stopped being in love with the other. Maybe she can be happy, and he has no right to be sad about anything that can make that happen. No right at all.]