My ex-girlfriend is coming, and I want to send a message to say hello, but we have broken up and he has a boyfriend, okay?

No, it will make your boyfriend suspicious and put your girlfriend in a dilemma. Think about it. If your girlfriend's period is coming, suddenly a man sends a text message to care about her. What's your situation? If you are more careful, your girlfriend won't believe you. So I suggest not. Hope to adopt. Thank you.