I can't explain it. Alpha/Beta/Omega fics just...unf. Love them. 

Fall In Ecstasy by 51stCenturyFox (Steve/Tony, rated E, 4.5k words)

There were...things on the internet. Most of them, well, made Steve realize that though people today seemed to be more accepting of differences, being an Omega or an Alpha wasn’t something you talked about unless you started up a website and made people give you their credit card number first.

My very first ABO fic, and the one that made me forever in love with it. Also, predisposed me toward bottom!Steve for life.

my fleeing heart by hoosierbitch (Clint/Coulson (with some Clint/Steve and Clint/Thor), rated E, 15k words)

Clint's heats have never been easy. This one is especially bad.

This was gorgeous and unbelievably painful and perfect. (Pain more or less resolved by the end. It'll be okay, I swear.)

Optimistic Decompression by exfatalist (Steve/Tony, rated E, 4k words)

To destroy all records of the Superhuman Registration Act before they could fall into Norman Osborn's hands, Tony Stark deleted his brain. In so doing, he forgot a lot of very important - and very terrible - things that he did. His life since has been spent attempting to reconcile how much his friends seem to despise him and knowing, logically, that he could have only ever acted according to his best judgment.

And while no amount of sensory input could possibly bring back such irreparably lost data, nothing was ever logical about the quiet moments when two people lay entwined together.

This is sexy and lovely and unbearably sad. Read it anyway. Then imagine how they'll figure it out if the author were ever kind enough to write a sequel.

We're All Goin' Home Satisfied by MoMoMomma (I don't even know, every pairing, seriously, though the Steve/Bucky/Howard one is my favorite, rated E, 41k words WIP)

There are things that designations accept; regardless of their personal feelings, they don't try to change them. Things like the fact that you procreate once you've found a mate, you don't let a red-zone Canidae bond bite you, and when a mate dies, you mourn and move on with life without them. The general public accepts these facts, generally without question.

And then there's the Avengers.....