what should i do?

I have a colleague. i am responsible for reviewing his work. but we are actually at the same level. no matter how much i have been teaching him, he still can not accept me as his reviewer. he always try to keep me out of loop by sending emails out without copying me or going to meetings without letting me know.
i talked to him and sent email to him formally addressing this issue as well. however, he just simply does not change.
i also talked to my boss one time, however, my boss is struggling with his own work, i also do not want to leave an impression to my boss that i am a complainer.

what should i do. not provide signoff until he provides me info.? however if i do this, my boss will eventually knows, complain starts anyways.