He keeps talking about his ex and still meets her. Though he says that they are just friends but meets her and refuses to tell his ex that he is dating you saying he doesn't want to hurt her but doesn't realize how much he is hurting you.
He keeps comparing you with his ex.
He doesn't want to meet your family and is always ready with some or the other excuses when you want him to come to meet your parents or other family members.
He refuses to show you much attention in public and he doesn't invite you to work functions where a date is required.
He also doesn't invite you to his family gatherings or occasions when he can introduce you to his family.
He won't introduce you to his friends until you're "on solid ground." But you've been dating him exclusively for six months!
He loves to go out with his friends and if you ask him to go out with you and your friends he says he needs to spend more time alone with you rather then in a group but doesn't go out with you either.
He never calls you up and when you call him up he says that he is busy. He also gives you standing instructions not to call him up at work saying he doesn't like being disturbed when he is working.
He spends more time online doing "research" than with you, but he can never explain what he's researching.
He claims he'll never, ever cheat on you, but he cheated on his ex in order to be with you.