The best rune for that is a stick. You hit yourself in the head with it every single time you think of not being loyal.
...jokes aside, what the heck kind of a question is this? Spirituality is not going to fix literally every single issue and answer every single question. Sometimes, the answer is something physical you must do youself.
If you find it hard being loyal to your girlfriend, maybe she shouldn't be your girlfriend. Or maybe you shouldn't be her boyfriend. Or maybe you should chat it out like normal people do. That is a good option too.
Nevertheless, if you want to instill new principles within you, the routine stuff, like your aura work and daily meditation, should put you at a good enough "vibration" so to say, that you have all doors open. You, then, need to step through them.