Moving on from a relationship. Therapy?

I am not able to get over someone who has made it very clear that they are no longer interested. Its been quite some time and they have reiterated the fact several times to me. In fact they never committed in the first place (It was complicated). Yet I am not able to get them out of my head. I find myself constantly thinking about them  and now tired of this all. Sometimes (like once a month) I have trouble falling asleep due to thoughts. I still keep trying to contact them  even when I know they dont like it and it almost always results in pain. I do not feel happy from inside. I am not taking interest in doing things. Sometimes it feels like there is kind of a burden on my heart. Other than this, life seems to be running normal but I never feel excited about things. I feel like I have grown habitual to this all but I don't know if it is normal. Can it be depression? Should I see a psychologist or a psychiatrist? Do I need medication or therapy?