Why lie at all?

When the picture is to ugly, look for another angle. I am thinking over and over again at this sentence, and I am trying to see another angle, but it doesn't work. I swear that the man who invented these words was drunk. And yes, only a man could invent such words. The commercial with the drunk man that sees a beautiful women through the bottle of beer, instead of the monster that was there a few seconds ago, pops into my head. 

Damn, that won't help me solve anything. I want to look at the sky, but instead I look at the grey cellar from over my head. The phone from my hand starts vibrating and it scares me a lot. I put it under the pillow and I hope that he won't hear it. F**k! I tell myself that I am a hypocrite, because I tell everybody who listens that I am against looking in someone's phone. But now, after reading the messages, I understand all the crazy girlfriends, and I agree that if something smells fishy this is the easy way to see where the smell is coming from. Fortunately, the phone stops making noise and he still is in the shower. 

I bang my head on the wall and I raise the phone at the level of my eyes. I can't stop reading from it. It's like an addiction, even if you know you shouldn't, you keep doing it. How is this fair? How? Why should someone lie? Especially to someone that says out loud that he/she can take anything but lies.
From BlaBla(him) to BlaBla(a she) 'Still on for the meeting tonight? I might crash at your place, cause I want to taste you a little bit..'. I can't read anymore and I let my hand fall near me. I hear him getting out from the shower and I put the phone gently under the pillow. He is singing a song, not suspecting anything. 

'Why are u staying so dull?' he asks me while he searches for a pair of underwear in my drawer. 

'Bored. Are you sure you have to stay at work tonight ?' I ask as naive as I could be in this moment. 

'Sorry love, work is work.' he approaches me naked as he is, and kisses me gently. 'I promise I will make it up to you' and before I have the chance to say anything he continues his search for underwear. 

I am remembering our first serious conversation, in which we were agreeing that we will have an open relationship, in which we can meet other people if we want. Why lie now? Why lie at all?