Help do I compare?

I feel I may not compare to his old gf they Are the top togther. She is a bit heavier than me but still she is beautiful with huge boobs and mine and small and I'm share she had a big ass to go with it she looks gorgeous to me!! I guess I'm worried I don't compare and I think he and I kinda look alike and it scares me that he may see that and that's why he is with me. An I just over thinking?