Is it normal to think about you best friends on-again-off-again ex

ok, so last summer, my best friend broke up with her boyfriend for the 16th and final time. she gave me his number and i texted him like crazy. we talked everyday from like 11 a.m. 2 p.m. when we came back from summer break (im in my last second year of college) we sort of avoided eachother. we texted less and less. i havent texted him since january. i still think about him. day and night. when someone asks me a question i answer and think what he would say. i told my best friend about it and she said i liked him. i didnt agree. i think about him and i cant help wondering if he thinks about me. do i like him? do i just have an obsession? is this normal?