Should stay?

Before quarantine I was a little insecure but I still felt confident enough to ignore little things(ex bf looks at another girl). I gained about 35LBS during quarantine and With that I also gained insecurities that are a challenge to control sometimes. My bf doesn’t break his neck to check out other women , but I see him look when we are at the gym or anywhere. I know he loves me and I love him but I’m not sure if I should be single. A part of me feels it not fair to put my insecurities on him so I should let him go but a part of me feels that it is also considered selfish because letting him go would break him. I’ve been hitting the gym and see a slight difference in my appearance which I feel confident... until I hit the gym and see all these pretty ladies around me or I see him look. Please, no mean comments, I’m already being hard on myself.