Lying is indeed detestable. It robs us of the information we need to make correct decisions. Most people have a built in lie detectors. The tone & content of the conversation is analyzed in much the same way as food is tasted. A lie makes us uncomfortable and we begin to suspect a deception. Judge Judy has famously said "If it doesn't make sense, It's probably not true."
Dont date people online that plain and simple only date people you really know and will see and anyone can lie on the internet and get away with it and if you really like him tell him to make you a fan sign with his face in it best way to tell if its really him Good Luck also he could get nervous and if you see him start to talk different or act different then hes hiding something from you usually but you got to watch some men can lie good without showing any emotions or appearance of it like eye movement and all the stuff like people do when nervous they can block all that out because they lied enough so its like they are telling the truth then they tell it so much they start to believe it after so long.
You must look out for body language when you ask him a question, he might scratch his nose, or it might just twitch. Usually when he looks up to the left he is making up a story. He also may not look you in the eyes while he is talking. But unfortunately these actions are very easy to suppress so you might not pick it up, and body language is not a very accurate science, so these "signs" may mean something totally different in your case