I have a question/first day of school experience

So I went to my old school and it didn't sucked because I get to go to a field trip. My old friend was there so it wasn't that bad. But I was like so focused on not messing up. To leaving my house alll the way to my school I had thoughts of "being back with my ex" or something like that like wtf? I said multiple times (trying not to panick because I was in public. Usually when I'm alone in my room I scream saying "NO I HAVE BETTER BOYFRIEND" trying to be as detailed as possible so this little shit can understand) I was getting the hang with it reminding these thoughts that I don't want my ex and I want my boyfriend. I was getting anxious and having thoughts and these feelings. Like I felt like those ex thoughts were right or I felt like I wanted them and I started to feel guilty. I knew that I would never leave my boyfriend with my ex! I had these messed up thoughts and it ruined me. It felt like I was going to cheat on my boyfriend. I don't understand. Those thoughts were so confusing and so awful. I tried to think of my boyfriend and remind myself again and again that I'm committed to my boyfriend NOT my ex. I had thoughts of ditching my boyfriend or cheat on him with my ex and it felt real and I was scared and I felt so guilty and sad. I had to figure out and try correcting myself for the ENTIRE trip. I got a hold on them for a awhile but I just felt bad. Did I do something bad? These thoughts felt genuine and real and the feelings felt so I can't describe it. Probably like a urge like the type of feeling of trying not to scratch that mosquito bite idk that probably sound worse. I feel like a bad girlfriend and awful I wish I felt that type of awful way before. It feels like I don't deserve my boyfriend. I told myself many many times that I have a boyfriend and I did NOT want to go to my ex. But ig I didn't do hard enough. There were many what ifs and many not what if. I promised my boyfriend I would never leave him. I would never do that to my boyfriend!! I hate that I don't feel genuine like wth!! This is my boyfriend I do love him dearly.