Everything goes to shit after that. The merger with Darby Int. happens incredibly fast and before Mike knows it, he has betrayed Harvey and lost his trust – lost him. He has also lost his secret to Rachel, the Harvard one, not the Omega one. He gets slapped in the face for that, twice, and afterwards he fucks her against a shelf in the file room. He likes her and he needs an outlet to fill the void of that all-encompassing loss that throbs inside of him. Plus, she is a Beta, which means that he can.
The following weeks are hell on Mike. Everybody in the firm can see that. There are dark shadows under his eyes and he keeps losing weight. He sleeps fitfully, if at all. His dreams during those brief periods of unconsciousness are either nightmares or blurry sounds and images. And very rarely he dreams of Harvey forgiving him for his betrayal. He hates those dreams the most because waking up to how things still stand between the two of them in the real world is pure torture. He just aches, body, mind and soul. He has no idea how to dull the permanent pain that keeps tearing him apart. He never knew that it would be like that, that anything could be like that. It is too much.
There's one situation that shakes him so deeply he feels something else but pain for the first time in forever. He's just about to make a copy of the letter of resignation he is planning to hand over to Jessica later that day when Louis suddenly appears at the photocopier. A second later he has seized Mike's note from him. Holding it in his hands and staring at it in disbelief while Mike fidgets at his side, Louis asks him why.
All Mike can answer is "Harvey." Because that is the truth.
When Louis launches into his speech about Harvey having always been Superman, having always worked alone, and how he isn't Superman anymore, Mike nearly faints. He has to lean against one of the file shelves for support. Does Louis know? How can he know? That has to mean that Louis also knows that Mike is-- No. There's no way he knows. He would never let anything that grave pass. It's impossible.
Mike manages to deflect Louis's attention by pretending to take advice from the Superman-turned-into-Batman-story – that he can redeem himself by helping Harvey win his cases, working his way into Harvey's good grace again. He swears to himself to even put up a convincing show, lest Louis catches on to what is the true underlying cause of his bone-deep weariness. He comes up with the idea to give back his brand new office all on his own, though.
When a tiny amount of his rational thoughts begin to surface again after his encounter with Louis, at least a little shred of sanity, Mike finds himself in a relationship with Rachel. He realizes that he has even told her that he wants to be with her. Mike is fairly certain that he will hurt her eventually, but she is the only thing that helps him keep the pain at bay. He knows he depends on her for that lest he goes insane.
Which is what makes him trust her with his other secret a couple of weeks into their relationship. She had withdrawn after the Harvard reveal and the hasty, slightly rough sex in the file room, not being able to cope with the injustice she sees in what he has done by lying to everyone at Pearson Hardman, well almost everyone, except for Harvey of course. And Jessica. Who found out on her own.
Mike knows that Rachel will stay with him once she has learned that he is an Omega and once he has told her what happened between him and Harvey in San Francisco. After the initial shock and a little recoiling, that is. He knows that she is going to love that he trusts her with a secret so deep and dark, with something that powerful. He knows she'll never be able to resist so strong a pull and he gives his biggest secret up to her to keep her at his side. He knows that most of all it will please her that no one else knows.
When all is said and done, Rachel is okay with it, like Mike has always known she would be. She has known for a long time, perhaps since her childhood days, that certain relationships between certain people can never hold the potential to go further or deeper than being comfortable with each other, enjoying each others' company and being compatible in bed. Mike knows Rachel likes him as much as he likes her and he knows that she enjoys being with him sexually, too. She understands why he needs her and she gets something out of their liaison as well. It works well between them. And there's no danger in it whatsoever – for neither of them – just fun and warmth and rows and understanding and everything else that constitutes normalcy in a relationship. Safety.
(They will even confess their love for each other later, and they'll mean it, too. Mike does love her and he curses fate (biology) for preventing them from really being together. He knows that that will never be possible, but he still wishes they could. Sometimes he fears he'll always be wishing for that.)
Working with Louis isn't as bad as Mike had thought would be. He knows that Louis wants to win him over and he's prepared to join him as his new associate. Harvey's never going to budge, after all.
He made that pretty clear when he told Mike that they were done. You and I – we're done. Harvey's calm and steady words keep ringing in his ears like the most brutal white noise in the history of radio wave transmission. Mike can't remember ever hating a sound that much.
Forgiving Mike and accepting him back as his associate is surprisingly easy in the end. Much easier than Harvey would have thought it would be. It feels like the pieces of the puzzle the world has become in the interim are finally shifting back into place, forming one whole from all its tiny, sharp shards and splinters. The easiness and the calm, simple logic of it make him queasy. He has a vague feeling that there is something he should see, something that he should know about, but he can't put his finger on it so he lets it pass.