Why is he treating me this way please help?

ive been friends with a guy 3 years and really like him. ive helped him with work exams, financial problems and lately hes turned on me. before he was very friendly around colleagues but now blanks me a lot and is quite cool towards me. he also knows i like him and manipulates me as in makes me call him and chase him if you like. why has he turned like this and how can i regain my self confidence and show he doesnt bother me even though it does please help