Top reasons:
1) It might take time for him to open up to you. This might be because of things he has kept hidden inside of him. You may try talking of his friends and relatives about what are his likes and dislikes and his childhood, college days etc. You might get clues to why he behaves the way he does.
2) He might not be too much into you. I know its painful to deal with this one. Reasons might be he doesnt like your looks, desires for some other qualities in a woman etc. However with time these reasons will be overcome and love will prevail!
3) He is with another woman. You know your options for this one ;)
There could be other reasons as well.. These are the top ones. All the best!
