Q: why is my macbook pro logging me out after a short time after logging on?

No. And likely will take more info and diagnosing as well as system log messages and what you have running, and installed, in the background etc.

And logging out? or something else?

Direct you to the proper forum for MacBook :

This forum deals with a desktop/tower 65lb Mac Pro

http://www.apple.com/support/macpro

General purpose Mac troubleshooting guide:

Isolating issues in Mac OS X

Creating a temporary user to isolate user-specific problems:

Isolating an issue by using another user account

Identifying resource hogs and other tips:

Using Activity Monitor to read System Memory and determine how much RAM is being used

Starting the computer in "safe mode":

Mac OS X: What is Safe Boot, Safe Mode?

To identify potential hardware problems:

Apple Hardware Test

General Mac maintenance:

Tips to keep your Mac in top form

Mac Running Slow: General Tips & Advice (Kappy)

https://discussions.apple.com/thread/4214422?

Mac OS X Help

http://www.apple.com/support/macbasics/

Isolating Issues in Mac OS

http://support.apple.com/kb/TS1388

https://www.apple.com/support/osx/

https://www.apple.com/support/quickassist/

http://www.apple.com/support/mac101/help/

http://www.apple.com/support/mac101/tour/

TimeMachine 101

https://support.apple.com/kb/HT1427

http://www.apple.com/support/timemachine

Mac OS X & Mountain Lion Community

https://discussions.apple.com/community/mac_os

https://discussions.apple.com/community/mac_os/os_x_mountain_lion?view=discussio ns

Recovery Mode

http://support.apple.com/kb/HT4718

ExpressLane

https://expresslane.apple.com/

Startup Manager: How to select a startup volume

http://support.apple.com/kb/HT131

Troubleshooting: My computer won't turn on

https://support.apple.com/kb/TS1367