If Nothing Else Works Out, There Is Always Unethical Approach
This is an unethical approach for how to tell if someone is cheating on you on Facebook for sure. If you are positive that your partner is hiding something, then use technology. There are multiple programs like keyloggers that can reveal your partner’s login data for Facebook. They memorize every keystroke and they are not detectable easily. After you get ahold of that, you can access their account and see for yourself if your partner is cheating. Also, there are other programs like mySpy that allow you to see your partner’s messages and message history from Facebook. You just have to find a way to install it on your partner’s phone or computer. Some of them may not be free, but that’s the price you have to pay for knowing.