Firstly, let me say that I am not an expert on cheating, but it did happen to me once. The clues I am going to give you today, are not at all proof of cheating, but might rightly get you suspicious.
The first way to tell if your man is cheating on you, is he shows you less affection, or too much affection. If your marriage, or relationship is falling apart, that could be a good reason to cheat on you, but at the same time, he might feel guilty about his cheating, and be extra nice, and buy you roses, to compensate.
You can start to get suspicious if your man says he is going to be somewhere, like working late, and then you find out that he was never there at all. This is especially worrying if it happens all the time. Then again, he might not be cheating, he may just want some time alone.
You can get a little worried if your man is a ladies man, a smooth talker, with a big sex drive. Studies have showed that a man with lots of testosterone is more likely to cheat, but this is just a genetic predisposition, it doesn’t prove he’s cheating.
You can tell that a man has a lot of testosterone, by his endowment, the amount of body hair he has, his sex drive, and interestingly, his ring finger will be unusually long. As long as his middle finger. Don’t jump to the conclusion that your man is cheating on you, by the size of his ring finger, but you may want to talk to him about it.