First of all, this topic was supposed to be in the GENERAL DISCUSSION or IDEAS AND OPINION section.
Coming to your question, You can realize a person whether s/he is in love with you or not, by his behaviour, acts and the way he communicates you. Loyality and sincerity is the most important point, you can judge someone in some minutes or some days. you need to spend time with him to thoroughly understand him and know his habits and then you can by yourself imagine whether he is perfect for you or not. Because the people, natures, behavior and circumstances differs.