another day in a troubled relationship

been thru a lot this past year with my relationship -- found out that my partner had been cheating on me with a co-worker -- when i found out i was devastated and decided to do some detective work on my own -- eventually found out what was going on, who the woman was -- even after confronting the two of them it continued for months, she was a married woman and didn't care that she was ruining someone else's life -- i've given my other half three tries now and not sure even this time if he will be true -- anyone out there had the same problem, if so, what have you done about it and can you ever trust them again?