If I was in a relationship where the sex had stopped for a lengthy period of time, I'd think I'd be asking myself some very serious questions. Sex is so important in a healthy relationship, and if it was to cease then that would be an indicator that the relationsip is in serious trouble. Rather than cheating on my SO, I'd try to see if we could work through the issues, and if that didn't work...I'd break it off with him. Then, I wouldn't have to cheat.