Easy you want your cake and eat it she is good enough for you for many reasons, bad to you for many reasons, this is not a healthy relationship if it was you wouldn't want to cheat and people here are telling you the right thing by their opinion and the actions they would seek and do.
You can't have it both ways, you want sex, she is psycho fixated on things but then again aren't you and your need to cheat.
To be honest she is not the only nice person in the world with so many good reasons to be with you really need to man up and leave the relationship BEFORE cheating or find another outlet for your sexual experimental needs.
Wake up and the others have offered you good advice so do your list of pro's of con's then make a mature decision, of staying or getting out.
Once you cheat you damage the other person for a long time and she is already tender dont be responsible for that emotional baggage.
Make a decision take the advice its given to help you see the errors and trials hence help you be someone worth knowing not a cheater it will haunt you later on
A mistake is always forgivable, rarely excusable and always unacceptable.
Robert Fripp