I've been with my boyfriend for 6 months now and he has always been a liar. I didn't care much when we first met because I didn't know I was going to have a relationship with him later and his lies seemed inofensive (he boasted on bigger grades, having taken part to some imagined events or doing something fabulous while he was in fact wasting time at home). I thought it as a sort of trying to get my attention, so I didn't take it that seriously.
However, when we got together everybody warned me to finish it as soon as possible because of his miserable past. When I talked to him about it, he got really angry and indignant that "others stuck their nose into our relationship." Though, he admitted the truth and told me even more, highlighting the fact that he knew what he did was totally wrong and he wanted to start life over. That day I was ready to break up with him, but I changed my mind after he confessed his mistakes and I have been listening everything very carefully since then.
By now, I haven't caught him on anything about this aspect (every time he talks about his past and repeats himself, the story is the same), he even moved further with talking about the past and I was very shocked to get to know he had a difficult childhood with his parents. He said that at the moment they're still fighting from time to time and that is why his glasses are broken.
A few days ago, I was to hear from his mother that a girl broke his glasses while he was at the university and this really made me question everything he said. Moreover, he's still lying about stuff: someday he bought some magazines for his mother and when I asked if the duplicate was for him, he denied and 5 minutes later he said one was for him. And the list can go on.
I understand his reason for lying at first because he barrely knew me, he didn't want to scare me away with his story, but why is he still lying into my face now? I agree sometimes he needs to lie his parents in order to get off punishment, but why would he lie to me? I thought I am trustworthy enough to hear the truth, and believe me, I'm not going to scream, not even raise my voice. I just want the truth, even if it hurts.
I just don't understand what's his reason for lying? How can I make him believe that telling the truth is better that lying? And how am I supposed to bring up this discussion without accusing and turning it into an argument?