They may tell you they make more money than they really do. They may tell you they are working late, but then come home smelling like booze.The lies they tell might have nothing to do with sex, but the fact that they are compulsive liars is itself a warning sign.Again, they might just be cheating, or hiding something else, but if they are lying all the time, you may be dealing with a sex addict.
Again, they might just be having an affair, but they might also be hiding a sex addiction.
Even when you're doing nothing wrong, they spend a lot of time being suspicious of you and acting like you're the untrustworthy one.
When a person has a habit of treating others badly, they often think that others are capable of treating them the same way. But if their sexual interests become all-encompassing, and if you are being pushed physically or emotionally beyond your comfort zone, then your partner clearly has some issues that may add up to sex addiction. Don't try to persuade yourself that nothing is going on. The worst place for you, and your addict, is the place that stays within the lie.
You may assume, after all you've been through, that they won't be receptive to talking, but you have some influence here.
Sure, if you come at them saying "You f*cking asshole, I know you cheated on me," you won't get an honest response.