I said happy birthday to my ex-boyfriend on his birthday! He didn't even reply to me

If you say happy birthday to your ex-boyfriend on his birthday, but he doesn’t choose to reply to you, then there is no need for you to waste time on him. He didn't reply to you, which is actually the best reply. He still doesn't have any feelings for you now. He even feels that you are just like strangers, so there is no need for you to send him any happy birthday wishes. Because to him, it is equivalent to a person who is stranger than a stranger.