Why wont my imessages send to a certain contact?

iv asked this question previously, less than a week ago. As everyone else would be, we are getting very fustrated as me and my boyfriend both have iphones, however when i send him imessages he doesnt receive them, and he cant send them to me but i recieve just normal messages to him. it's been going on since last wednesday and we have tried everything!!! our messages send to everyone else but each other. I had an answer for him to just reactive his omessage and delete our thread but now that won't even work anymore and it is very fustrating as he is the main person I need to text. please help.