<human>: Summarize the given text in a few sentences.

So I have been with my current gf for almost a year now. We've had our separate ups and downs but our relationship has remained strong through it all. We communicate very well most of the time and we haven't even had a fight yet. The problem is that over the last couple months I have become very insecure. 

For some background information I used to play football and lift weights and be in pretty damn good shape. I was confident at this time. Which was about 4 months ago. However 4 months ago I received a very serious concussion. I can't ever play again and I had opportunities to play in college( I'm currently in high school).  Ever since then I've been dealing with some mental issues. I am not as emotionally stable as I once was and I've fallen out of shape big time. I think I don't have as much self worth because I based my worth on my athletic success. Within the past couple of weeks I have had panic attacks and crippling insecurity. Through all of this I have done my best to not project this on to my sweet and loving girlfriend. I used to never care when she went out with her guy friends. Now I feel panicked when she does. I feel scared of losing her most of the time. It's like the rational part of my brain knows she's never hurt me and never will but the irrational side keeps thinking she's with someone else or that I've always done something wrong. I get jealous when she goes out and become really clingy. I have tried shutting it out but it just doesn't work. I really need help trying to work through this not just for my relationship but for my own mental health. What can I try? I don't want to go to therapy before trying things on my own.
<bot>: I used to be confident and trusting in my relationship with my gf. Now I'm becoming insecure and jealous after a semi recent head injury. Looking for ways to improve myself and my mental health. Help?