In order to fix a problem, you have to acknowledge it. Speak with your partner about how their lack of affection impacts you. One example of a way to tell someone that their lack of affection is bothering you is to say, "I have been feeling sad because I need more affection than I'm receiving in this relationship. It would make me really happy if you were willing to work on becoming more affectionate." If this still doesn't produce the results you're looking for, it might help to enlist the help of a sex/relationship therapist.