My boyfriend tells me little lies...?

My boyfriend is amazing to me. I finally find a truly nice guy and he treats me so well. The only thing I don't understand is that he sometimes lies to me. And when I mention something about it... he still won't admit to the lie. An example,he wanted to take me out to dinner but I knew he was kinda low on cash. He really insisted. I told him that I didn't want him bumming money off his mom for gas, if he is taking me out to dinner. He said he was more than okay with money and not to worry. We eat. He gets gas. Before payday I know he's broke and low on gas. All of a sudden he magically has 20 dollars. I asked how he said he found it in a jeans pocket. Fair enough. 3 days later his mom is asking where her 20 is that he owes her. I asked him in private about it and he said his mom was making up lies. He lied cause he don't want me to feel bad but I told him I don't like being lied to regardless what its about. A lie is a lie. Then he has a facebook. So do I. We aren't friends on facebook and I don't care either way. We practically live together so its no big deal. I always ask him why he doesn't request me and he tells me he never goes on facebook, ever. That its been well over a month. Fair enough. Well his mom just made a facebook last night and he accepted her friend request since then. Umm... so he is going on facebook? What's the deal here. I know he's not cheating.. but is he hiding something? I trust him a lot. More than I ever trusted a guy before. But what's the deal? Any suggestions? I don't want this to turn into a fight or anything.. I'm just curious.