How can I overcome my insecurities in my relationship?

I recently read a question about your S/O being out of your league, and it kinda made me think about my own issues. I am currently in a wonderful relationship with an incredible man! It’s been an amazing nine months, and he is everything I could want. He is funny, smart, thoughtful, chivalrous, handsome, I could go on and on. Perfect right? Well, I am plagued by this self doubt about it. All of his exes realized what idiots they were to let him go, and still want him. Everyone adores him (family, friends, co-workers, etc). Other women want him. Don’t get me wrong, I am so proud that I am with someone who is so admired by his peers and family. But I am left wondering why this man is with me!? Note: I am not a dud. I would say I am a smart woman (I have two degrees), fun, motivated, not modelesque but cute. I am normally pretty ok with who I am and what I have to offer, and I have never in my life thought that someone was “out of my league” or too good to be with me. I am baffled by this insecurity. Have any of you dealt with this? How do you overcome it? I feel like I might just be in awe that I am in this incredible relationship, but still would like the doubt to leave. Help please :)