He does not pick up your calls or return your texts and emails in a timely manner. You find yourself making excuses for his lack of connection. Avoidance is a simple and clear message that he is not seeking your attention.
He does not involve you in his family life or make an effort to introduce you to family or friends. He does not invite you to social functions. He does not make himself available to meet your friends and family.
He is too busy to set aside time to spend with you; he has other things going on. He does not want to make plans more than a day out. You may be more of a convenience or a distraction than relationship material.
He does not bring up the future. Even if you are not planning for a wedding and children, he will not plan for your next vacation or long weekend.
Not every man knows how to express his feelings directly, so he continues to be ambiguous. He does not clarify his feelings and leaves intentions vague. He may not fully understand his own hesitation.
He talks about other women and shows an overt interest. He stays close or initiates contact with an ex. A man who is interested in you will be paying attention to you.
He has a set of reasons for not being more involved. His reasons leave little room for debate, such as focusing on his career, hurt by an ex or he is too busy to give time and energy. If he were interested, he would find solutions, not excuses.
He is less interested in intimate contact or only wants to be with you physically when it is last minute or he has been drinking. The amount of contact is less frequent or has stopped.
Go with your gut feeling. If you think something is wrong, then it probably is. Your friends are most likely seeing signs as well and may try to tell you.
It takes two to communicate intent. Are you sending signals that he is misreading? Are his behaviors in response to what you are putting out there? Examine your own signs to see if he may be reacting to you.