I don't "get" my species either!

Take me for example; I'm a bit slow on the uptake when it comes to romance, YEARS (10) before my bf and I started dating and we were just best friends in high school; he had to point it out that I was inlove with him, and he with me!

No really, he said "you love me" I said "duh" he said "no. you love LOVE me... think about because I love LOVE you too"....
Granted I was young but sheesh he was right, and had he not pointed it out then, we probably would've not been together today.
Next point in case: My brother who is a good looking guy has washed himself of appearing to be the nice guy he genuinly was. Long story short, our brother and father died and lil bro turned into an a.s.s... since then? Girls fall over their feet for him to notice them

The more he ignores "her" the more "she" tries to prove her worth! i.e bakes for him, buys him lunch, and just persues him like mad!
When we started noticing this we ran some "social experiments" and for some reason women (atleast the ones in his age group) are not "playing games" regarding wanting what they can't have, some of us just seemed hardwired that way!
He had a longterm gf at one point whom he ended up dumping because the nicer and more supportive he was, the *****ier she became

Have no idea why "nice" is a repellent for some women folk
Uhm so I went off on a tangent

sorry. My point is, women and men are weird creatures, I don't have any fantasies of "understanding" my bf, I believe in practicing acceptance rather than understanding.
And more importantly, tell her how you feel instead of kicking yourself night and day. What have you got to lose? She's not yours now, so you can't lose her, yet have everything to gain.
And yes, I know how badly the sting of rejection can hurt, but I've never read of anyone dying from it, its worth the risk, IMO true love is worth anything.
So sorry this is happening to you, I've been in very similar shoes