I'm sure I'll think of more, but there is "He's my Best Friend's Boy" Which is always a good read.

You can get the PDF here:

http://www.4shared.com/get/bu36Eznq/Hes_My_Best_Friends_Boy.html

There is also this list, where they are with someone else but they cheat with each other:

http://j2-recs.livejournal.com/tag/cheating%20together

Thank you! I've read He's my Best Friend's Boy, loved it. And I've checked out those recs xD

One Small Step (http://sandymg.livejournal.com/60559.html)
Summary: Jared has had a secret crush for months. But it’s not like publishing genius and gay activist Jensen Ackles is going to notice the tall, weird guy pushing the mail cart. So when Jared’s best friend and Jensen’s assistant, Sandy, tells him that Jensen is getting married in one month to a fellow activist -- something about being the first gay couple to get married in the state -- Jared knows some things just aren't meant to be.
And now Sandy is insisting that Jared help her plan the wedding. She thinks it’s a good idea. Jared thinks she’s nuts. Because the only thing this could lead to is heartbreak. Right?

Lips are sealed (http://trueshellz.livejournal.com/88896.html)
Summary: Marketing assistant Jensen Ackles hates flying and one particular flight means that he blurts all his secrets to the stranger next to him. But that stranger has a bigger connection with Jensen than he thinks.

Curtain Call (http://insane-songbird.livejournal.com/23885.html)
Summary: Jensen has worked as an actor and dancer for the same musical company for a few years already. As young dancer Jared is hired, Jensen takes him under his wing and encourages him to want more than just holding a spear. But when the next shows roll around, Jensen is hit by fate and Jared takes over his part. Wary and resentful Jensen starts the new season. But everything is put to the test, as the two of them need to work together to see the new play kick off.

Bring Me to Life (http://ally-fics.livejournal.com/10338.html)
Summary: Jared’s a shy young man, whose life has never been easy. His father hates him, his mother drinks her sorrows away and his husband Paul treats him like he is nothing more than a beautiful toy. When his husband has to go away on a business trip to Europe for two months, he sends Jared away to a ranch in the middle of nowhere to keep him under control. There, Jared meets people who show him what love, friendship and loyalty mean for the first time in his life. Can he escape his life and finally find some love and happiness for himself?

Something Real (http://ally-fics.livejournal.com/29304.html) This fic is a WIP.
Summary: Jensen has it all; a great job, a loving boyfriend, an amazing family. Then he wakes up to find out that it’s all been a dream.

I Wanna Know What Love Is (I Want You to Show Me) (http://crynintherain.livejournal.com/13579.html) This fic is a non-AU.
Summary: Jensen is with Jeff Morgan and happy. Jared is in love with his green-eyed co-star and oblivious.

A Devil to Help Me Get Things Right (http://doodle-writes.livejournal.com/23394.html)
Summary: It was in moments like this that Jensen knew that they would be together forever. Nothing would or could break them apart. Jensen was wrong. At 19 he was in love with Jared, full of plans and hopes for their future. He didn’t count on dropping out of college and driving Jared away with cheating and drinking being part of them. At 30 Jensen wakes up with retrograde amnesia, his last memories of being 19 and happy. As he struggles to regain his memory and find out who he is, Jensen has to face the harsh truths of who he became and how he treated Jared. Determined not to make the same mistakes again, Jensen starts to get his life back on track and try to win an engaged and angry Jared back.

I noticed that you did not have an infidelity tag. So, I thought you should know that "One Small Step", "Bring Me to Life", and "A Devil to Help Me Get Things Right" all some infidelity in them.

Thanks for all those! I've read them all and that's why I've been looking for more xD