I hate to disagree with you, but you may not always know. My job requires me to be gone sometimes for weeks at a time. My ex and I had raised our children and were alone at home. We had a wonderful sex life and were soul mates, or so I thought. We had just moved back home and built our dream house and seemed like we were living the "perfect" marriage. I was completely destroyed when I found out she was cheating on me. She not only was cheating, but walked out leaving me over $250,000.00 in debt. You think you would know, but there was NO indication that there was anything wrong in our marriage. I"m sorry, but I don't thing you will always know, if you love that person you are not looking for those clues and sometimes we have blinders on for love.