It is hard to say, but most of the time it is because you have bored them to death and they are looking for what you both had when you first hooked up. There are alot of people that put up a front then change not to far down the road. All I got to say about that is be your self form the start and it will go alot better. Dont always have sex in just the bedroom. That gets really boring. If you are a lady you will let him lead, but if he dont lead find some one else. For the one that think I am a cheater well I have never done that.