[@Kyux] I'm back:

As a symptom of your guilt you may feel this way because in your mind you may feel like you are 'cheating' on them in a way. But you probably would never do it IRL, but you feel guilty because it is a betrayal of trust in your mind.

You may just need to spice up your love life? Try different things as a couple be it romantic or carnal. Tell the truth if you want or try to be more involved in your love life if you aren't.