I am sexually attracted to people other than my partner

Here I will work on the premise that humans are not hard-wired for monogamy. You can reject that premise if you want, and I can't see how that will be anything but detrimental, but discussion on this is for elsewhere, and I will not take part in said discussion, here or elsewhere. So go write a blog post about it if you must.

People in long-term relationships will invariably report some degree of sexual attraction to people outside of their relationships. This is natural, and to be expected. If we agree that humans are not hard-wired for monogamy, then it stands to reason that such sexual attraction in and of itself is not a sign of a deteriorating or flawed relationship. It is usually coupled with a decrease in sexual excitement with the partner, and neither is a sign of incompatibility. Simply put, you need to be able to commit to the relationship and recognise that it will bring you greater good than multiple sexual partners. If you don't agree that your current relationship brings you greater good, then there is no shame in this, and you are probably right. You should end your fucking relationship before you act on any of this sexual attraction, because cheating is a disgusting act and anybody who would have the act of cheating associated with them, I would have hanging by their intestines from my front porch. It is never, ever justifiable, never an appropriate course of action, and it is not a 'leveller'. That is, cheating does not 'even the score' or 'cancel out' the bad deeds and misbehaviour (that wasn't cheating) of your partner, rather it puts you infinitely lower and beyond redemption.

If you find yourself desiring sexual relations with another, or emotional relations with another that run contrary to the terms of your relationship, you need to have a serious think about your relationship, what you are lacking, and if and how or if not your relationship could be refashioned to provide what you are lacking. Hopefully, this thought results in a positive action of either appropriately amending your relationship, or ending it. This should, of course, involve discussion with your partner. This will be very difficult, and I can't guide you through it and neither can anyone else. Needless to say you need impeccable communication skills for it to be an effective and healthy discussion. If the 'positive action' you reach is following through with your urges without ending your relationship, I'll direct you to a few suicide blogs and try to keep my blood from boiling with such vehemence that it melts my arteries like cellophane.

If you have cheated, there is hope for you yet. In my experience and the experience of everyone I know who is worth listening to, the deficit in your character that allowed you to cheat will not be overcome while you are in a relationship.