If you find out they're cheating, finish it.

If you find out your partner has been cheating, then walk away. Really. Its just not worth the hurt and effort need to forgive someone and you'll never rebuild the trust. Better to start again with someone new. If you stick around your partner will soon try to point the blame in your direction. 'you didnt give me enough attention/I thought you were leaving me/it just happened so there must have been something wrong' blah blah blah. Lets face it, they are the manipulative one in your relationship right? Before long YOU will look like the bad person for 'not being able to forgive and forget'

Would you go back into business with a partner who had cheated you? No - of course you wouldnt.

Of course, if you have kids or are married, it becomes a bit harder and the rules are different. But if you just have a girlfriend/boyfriend then walk. You'll be better off in the long run. And this tip counts for DOUBLE if you are engaged to the cheat!