Insecure about breast size?

Ok-so this might be a little TMI. My fiance’s ex is really ghastly. Anyhow, she has got these great ginormous boobs, whereas i do not. My fiance’ is a “boob man…” I am not as abundantly endowed, unfortunately. I realize he is with me, not her, so i shouldn’t worry…but she makes sure to mention them ALL the time and really throws them around alot. (i.e. bending over in front of him purposely, wearing shirts with HUGE amnts. of cleavage at family functions, talking about bras etc. etc.) They have a kid together (as do we) so just “not being around her” or ignoring it is a no go. She even breastfed their child, and whipped her boobs out at every possible opportunity, and THEN tried having conversations with us (as opposed to going in the other room or SOMEthing)...(and i promise you this is all on purpose, everyone has noticed-not just me) Even though I know I am better looking than her (not conceited, just a fact) ...I have been feeling incredibly insecure about my boobs b/c of this (where i never was before) to the point where anyone even mentions “big boobs” around me and my blood boils!! I have been feeling really down about myself, and I don’t know how to stop it short of getting breast implants (which i can not afford). I know my fiance’ tries not to look/notice but really…what man wouldnt? (i cant even help it myself) What can i do about this? any suggestions? how can i fight this? I think it just makes it worse knowing my fiance’ is really into large breasts, and that i dont have them. And yes, I do realize how immature this all is but I cant help myself.

They’ve over a year apart…but she got pregnant after they broke up (total accident-stupid mistake) nothing sheisty going on, she’s just pretty hung up on him still. I think she always will be maybe. We have been together for 3 yr. now