Anxiously Attached to my girlfriend

I struggle very deeply with relationship anxiety on a day to day basis.

But there is nothing that comes close to the anxiety I experience pertaining to my relationship and the constant fear of abandonment and being cheated on. I (23M) have been dating my girlfriend (21F) for a little over a year now, i graduated last year around this time and have been working full-time since, while she is still in college and in a sorority. 

Every single day while i am at work i am consumed by this horrible and deep fear that while I am here, she is at her apartment cheating on me and that she is going to leave me. All of this comes from a deep rooted trauma withing myself due to my previous girlfriend cheating on me just shy of a dozen times by the time it was over all without me having a clue until after things had ended. I spend each day and frankly each moment that we are apart completely paralyzed by the thought and unable to be present in any other part of my life.

I just recently started up therapy again to try and build the skills to combat this, because i can recognize that i have no actual evidence that she is actually doing any of this but i just simply cannot redirect my mind away from these heinous thoughts.

I recognize that this constant state of fear I subject myself to is not healthy for me, and it is not healthy for the relationship. I just want to stop straining our relationship and ultimately deteriorating it all because i simply cannot get over my own overthinking and trauma responses to certain situations. I'm not sure what I can do, my therapist recommended trying to redirect those negative thoughts with positive thoughts of her and our relationship when they come into my head but I feel as though that is a lot easier said than done. Just today at work, i have spent nearly the entire workday stressing over this stuff completely unable to be productive over the last 5 hours and it is driving me mad. I shouldn't be this obsessed with what she is doing every waking second of everyday, i don't want my world to only revolve around her, i want to be secure with my own individuality and be comfortable by myself, whether or not we are in a relationship.