Did I really cheat on my wife?

Try to be true to your marriage vows and avoid compromising situations like the one you had with her friend. If your wife can do anything to help put the spark back into your marriage then you owe it to her to try and talk with her about it. Don't just blind side her some day with the fact that you aren't happy and feel unsatisfied. As for her friend, she's no friend to your wife what so ever to be playing games with you. Trust. ';-(