Most Helpful Guy
I don't get it, you know he's lying but he won't admit it? If you know for a fact (you saw him at a party with your own eyes and he said he wasn't there kind of thing) that your BF did something, why do you need him to admit it? If there's any question about it why can't you take his word?
When I was a young man my stepfather would ask me questions he already knew the answer to, just to catch me in a lie. How mean it was to put me in that situation, it would have been better to just say I saw you at... what do you have to say about it? Instead of asking where were you?
Do you understand, if it was something that you KNOW confront him with your fact, if on the other hand you just think it's true (your girlfriend saw so and so who said such and such) mmaybe he's telling you the truth.