AIO: My girlfriend made a list rating her male friends while we were dating, and I feel sick. Am I overreacting?

Please read context before the problem!!! I know this is a lot of writing but I really need to know if I'm overreacting :(

Context: I made this account because I don't want anyone I know to see this!! So I (17 M) have been dating my girlfriend (18 F) for well over a year now. To give some background, most of our relationship was long distance, but we do live with each other during the summer. I would like to say that our relationship is very strictly closed, as both of us are very loyal to each other. One thing to note however, is that I'm a jealous person. Of course, I'm in no way abusive because of that, it's more like I get a bit jealous if my girlfriend hangs out one on one with her male friends. My girlfriend knows this, and always reassures me in case I ever feel uncomfortable and / or jealous. One thing to note that will be important later is that during the month of November, my girlfriend was struggling a lot both physically and mentally, which I did my best to help her going through that rough time. She was also the section leader of her marching band during that time. --> This will all be important later.

Problem: For this past few weeks my girlfriend has been staying in my place. We both like to do this thing were we leave cute messages somewhere for the other to find. For example, maybe a strip of paper with a cute message on the bed, a google search on the other person's phone, etc. So I've decided to leave a cute message for my girlfriend on her notes app. She is totally fine with me using her phone no matter what! We have established that we don't really care if we use each others phones. When I opened her notes app to write the message I noticed that one of the notes made in November was her rating all of the cute / ugly guys in her marching band section. There was a lot of guys in that list. Some that I knew she went out to dinner with. Now this is the part where I need other people's judgment: I feel terrible for what I saw. I mean, during that month I did my best to help her. I put her over school and I spent money to help her both physically and mentally. Plus, one of the worst parts about this is that, I know that she went out to dinner with someone, if not all, of these guys. I feel absolutely terrible and I really need to know if I'm overreacting. I need help guys :(. Also what should I do about this? She just came back to her house and we are long distance again. I really don't know if I'm overreacting. What should I do?