Today is Valentine's Day. I want to send a message to my ex-boyfriend and ask him out. What can I say?

You can ask him how he is recently, and then say whether he is free today. If he says he isn't, don't make an appointment. Tell him you want to ask him out when you are free. Sometimes it's unnecessary to say so much. It's better to say it directly. Even if you can't be lovers, it's ok to be friends and hang out.