How to Know When Your Ex-Boyfriend Has a New Girlfriend

Research from Harvard University shows that men in committed, romantic relationships have lower testosterone levels than singletons, so there are some hormone-related behaviors you can look out for to tell whether he has someone new he is serious about.

According to the study, published in "Hormones and Behavior" in 2003, men who were in a serious relationship had 21 percent lower testosterone levels than single men. High testosterone levels are usually associated with aggression and dominance. If he's suddenly letting you win at pool, this may be a sign that he's met someone else. Generally being less competitive and more submissive might actually mean that your ex has moved on.

Although he may be prepared to let you win at games, this doesn't mean he's still interested. If you notice he's not smiling as much and doesn't hold your gaze for long, those are signs that your ex may be with someone else. He might be trying to demonstrate to you that you are now no more than friends, and biologically he's also less likely to show interest in any other females. Men with lower testosterone levels showed less interest in ladies in general, smiled less at them and made less eye contact, a 2011 study showed.

Previously your ex may have always rushed to answer your calls and responded immediately to your texts. If you find he is always "busy," he may have found another girl. If he does answer the phone, but sounds cagey, she might even be sitting beside him when he takes your call. Don't rely on him telling you honestly that he has found a new lover, as research from the University of Bonn showed that men with lower testosterone were more likely to lie.

You may be having a casual conversation and find out that your ex-boyfriend has suddenly started a surprising new hobby. You may wonder why he would suddenly take up hang-gliding when he's afraid of heights. If your ex has new interests that seem out of character, it may be due to the influence of a new flame. If he's really prepared to spend his time and energy doing unfamiliar things with his new partner, it means he has firmly moved on -- and so should you.