Love and LURVE
Why do I think people cheat in relationships? I think you lose the NRE - new relationship energy. It's normal. It always happens. And your partner doesn't give you that lust feeling, that INTENSE LURVE anymore. And then, you're an arse for not appreciating the other things that are there in its place - you've taken the time because of past LURVE to really know them, to build history, share common values and goals. Those things are the things that that insignificant LURVE leads to. So you, idiot, think LURVE is the goal and wander off looking for more of it. OR once the LURVE fades you find they're an arse and you have no partner-choosing skills so you wander off aimlessly.