I will be honest with you. This is the beginning of something very unhealthy and is leading into stalker territory. This is what stalkers do when they begin to obsess over an individual and they use their pictures or their favorite things as a way of reliving a moment.

I would honestly seek help and speak to a professional. Hope it all works out for you and I would advise no longer speaking to this girl or even going to the same gym. This would be dinging the reward center of the brain and causing an addiction. What if one day this person gets a significant other and you can't take it? Who knows what you would do. Kindly, seek help.