Question: how to stop thinking about someone obsessively?
Answer: Take them off their pedestal. It is so easy to overlook someone's flaws when we are attracted to them. ... 
Do not let their opinions define who you are. ... 
Get a support system. ... 
Realize that you don't need them in your life. ... 
Practice mindfulness. ... 
Distance yourself. ... 
Trace the source of your obsession. ... 
Find something new to do.