Up until near the end of your story I kept thinking "Maybe he's secretly (even to himself??!) gay... I mean, kissing her makes him *nervous*? Going down on her squicks him out... so, what, he doesn't like vaginas?? But he really likes receiving oral... maybe because then he doesn't have to deal with her woman-bits like you do in vaginal intercourse???" But then I read the part about the porn so unless it's gay porn I guess that theory is out the window.
Maybe he's just kinda-asexual, in the sense of not getting that excited about the idea of physical intimacy with another human being? But that doesn't excuse ignoring you at other, non-sex times, in favor of tv and videogames... ugh, how boring, at least he could ignore you for a wider range of more stimulating, enriching activities?? Is he, like, depressed or something?
Couple's counseling is definitely a good idea. If he doesn't understand your needs, that can be corrected. But it seems like with all your explaining, the long letter, etc, he MUST understand by now... but maybe he doesn't really get how serious this is for you? Maybe if he really understood that you might actually leave, that you are contemplating divorce as an option? Yeah, counseling. Maybe he can learn to be a better, more attentive partner. Reading that Love Languages book is also a good idea.
I think you should lay it all on the table. Tell him how deeply unhappy you've been and how often, how it's just this ongoing struggle that doesn't seem to be getting better, how this has affected your life path vis a vis the college thing, how it's affected your self-esteem. AND tell him about E, make him promise not to be mad at E but go ahead and tell him about your crush, and that you honestly want to be with both of them and think it could work but that it's NOT a way to run away or avoid these various serious problems, just another thing going on at the same time. Tell him you guys don't have to make any decisions right away, and in fact should absolutely NOT make any decisions right away (it'll be too colored by still the other stuff), give him some things to read. Tell him before you talk to E, tell him you won't talk to E if he wants you to wait while the two of you work out what to do.
Honesty is the only way to go here. Then you guys can figure out the best path together, like real partners should. Isn't that the whole idea of marriage, partnership (your brother is wrong, by the way... an open marriage that's honest and strong is absolutely real, and is much more of a real marriage than a lot of the shells of marriages out there)?