In order to know if a married man is serious about you, there are several key things that you can look for and pay attention to. First and foremost, you need to see how he treats his wife. If he regularly neglects or mistreats her, then it's unlikely that he'll be serious about you. Additionally, take note of how much time he spends with you compared to his wife. If he's constantly blowing off his spouse in favor of spending time with you, it's a sign that he may be serious about you. Finally, listen to your gut; if something doesn't feel right or feels off about the situation, it's probably because it is.