Why do guys lie?

Sophia
I have a friend who I would hook up with basically every week. We both in college so he told me that he doesn't want a relationship right now and I was okay with it but with that being said he treated me like his girlfriend. We are completely honest with each other about everything since we're basically like best friend. But the problem is his ex girlfriend constantly bothering us, she would crazy calling him the middle night, come up to me and start calling me names and just do anything she can to get rid of me. He kept telling me how much he hated her and how much he can't stand her. Last night I accidentally got stranded in the middle of the party around 1:40 am and could not make it back to my dorm so I called him up since his house is a walking distance from the party, he said he's not home right now and he'll text me later. So I walk in 10 degrees outside weather to wait outside his front porch, I kept calling him and he wouldn't pick up the phone. Finally at 3:30 am he came home but he also bought his ex girlfriend with him. I didn't say anything except walking away. He didn't even bother to look at me. I was walking around the town all night and the next morning he claims that he was too drunk to see the messages and didn't realize that I need a place to stay and that's his ex girlfriend was just walking him home. I know it was a lied and he just kept lying. He's not my boyfriend so I have no right to be mad. I just don't understand why most guys that I talked to always do this to me.