im not very good at putting my point across in 'print' im better if you speak to me in person but my favourite sex advice columnist can do it for me:

http://www.thestranger.com/seattle/SavageLove?oid=26100

everyone should read savage love anyway.
there are more examples but i cant be bothered to go through his entire archive right now (though i have read almost his entire archive, from the bottom, very amusing, educational, good for sexual emotional intelligence and v. interesting re: sex politics in america)

ps. i've never cheated ona boyfriend myself, just in case you're all thinking im some jezebel desperately trying to justify myself