I'm going to ask my boyfriend for transparency
Does he lie often?
He lied to me about his ex.
Normally it's wrong to be too controlling or demanding of your significant other.  You should let him have his privacy, but if he directly lied to you about something important, you are right to ask him to be more open and honest.
I know and I'm going to make sure that he understands that.
That is good you can set boundaries. Try not to come off as controlling because it can cause even more secrets in your relationship and no one will be happy.