I miss my ex-boyfriend very much and want to send him a text message, but I don't know what to send.

You still miss him for so long, which proves that you still have him in your heart and you still love him. If you want to stay with him, you can call him directly and ask him how he is doing recently. I'm worried about you. Do your best. I think if he still loves you, he will definitely come back. I wish you happiness!