The first thing on my mind is jealousy: If you think, his loss of interest is a symptom and you want a change, meet with friends more often and introduce new people, new activities into your life or try to change your image (haircut, a few details in clothes). As for the first piece of advice: When I feel ucomfortable and not admired enough, I go on a few sites dating services and social networks and I just chat there, all those nice things and compliments people tell me, make me feel happier and then when I tell something about them to my bf, it renders him jealous and he starts being attentive and nice to me again :)