Um hi I'm new to this and kinda looking for advice I guess? I experience extreme jealousy over my partners exes.

like it makes me feel bad because he said a past partner will understand him better than anyone ever can and for some reason I can't accept that I know he loves me but I cant shake this voice that just says "go back to him then if he's so great"

And he's amazing don't get me wrong, he reassures me that I will understand him and that he loves me and not the ex and he's just an amazing human being 

But it's just me feeling jealousy that I wasnt the one to understand him better, that the ex gets to understand him more and it's just not fair and that I won't ever get to love him I guess? 

And this is me being stupid but whenever I hear his name I feel a slight twinge that he's better than me somehow?