Cheating is never okay, if you want out of a relationship be a man and talk about it and call it off before you go out and hurt someone.
My last relationship was eight months long, and the whole time I thought my boyfriend at the time was the most wonderful person alive and so trusting and caring. However, after he dumped me I had his phone one night and decided to go through it and found out he was cheating on me for a good chunk of the relationship. Trust me, it's an awful feeling and if you by any means think it's 'okay' than you are clearly not meant to be in a relationship.