Could not avoid it

Since I am going to meet my girlfriend today I have planned to take off . My boss will be angry with me if I did not inform him about my leave. But the thing is if I call my manger through phone he will convince me and asks me to reach the office in 30 minutes. So I have planned to send him mail and inform him that I will not be working today. Since after a long time my girlfriend has asked me out I could not avoid the situation.