Why doesnt he ask me how my day is; but he asks his best friend?

Might not care how your day is.

🤔...............How is your day going?.........That was easy......

Guess you are not his best friend

He is probably wondering you don't ask how his day was...👀

We need more information

Because some men don't know how to treat their partner. He either doesn't care or didn't think to ask. The true test is asking him about it. If he apologizes and starts asking you, cool. If he acts offended, he doesn't know wtf he's doing and it's going to get worse.