How do you say hello to your ex-boyfriend?

It depends. If he talks to you first, you dont want to sound extremely happy about it. Sound calm and natural. For example if he says, "Hey" you may want to say "Oh, hi." to start it off. But if you want to text him first, you could start by either 1. Ask him a question you know he would know. About anything, just not about relationships. Or 2. Pretend that you "accidentaly" sent him a message instead of someone else.