As reported on WebMD, according to authors Greg Behrendt and Liz Tuccillo, the authors of the book "He's Just Not that Into You," there are many ways to tell if your man is losing interest, and it doesn't mean that you're not a great catch or a spectacular person. It just means that for some reason, he's just not that into you. A few signs that Behrendt and Tuccillo reveal are that he stops asking you out, he stops calling you, he stops dating you, he stops having sex with you and starts having sex with someone else, and he only wants to see you when he's drunk.