Here's an eavesdropped conversation between two boyfriends at a coffeeshop, transcribed from a recording by a surreptitiously placed iPhone.  (Warning: content is controversial and will be deemed offensive to many readers.)

    First man: "Why won’t you kiss me?”
    Second man: "Because I smell cum on your breath.  We promised to be monogamous, and you’ve sucked off another man.”
    "He isn’t just another man—he’s my brother.”
    "Your own brother?”
    "Why do you sound so surprised?”
    "Well, jacking off together as kids is one thing.  But oral sex?”
    "Wouldn’t you do anything your brother needed you to do?  How exactly do you define brotherly love?”
    "Certainly not as brotherly sex.”
    "But you can’t separate sex from a man’s profoundest needs.  A man’s sexuality is his highest expression of life.  What could be more important than helping a man to fulfill his sexual nature?  When my brother needs mansex, I have to be there for him.”
    "But why does he need you for that?  Why doesn’t he call on a fuck buddy?”
    "Blood is thicker than water, and cum is thicker than blood.”
    "Well, the blood connection of brothers gives them a true intimacy—what other masculine relationship could compete?  I’ll give you an example: when my brother and I sixty-nine each other, we’re so in synch that we ejaculate at exactly the same time.  Even our individual squirts of jizz are synchronized.  It’s wild beyond description.”
    "You sixty-nine each other?”
    "Of course.  Whatever he wants me to do, I do it for him.  That’s the meaning of fellowship, of camaraderie, right?”
    Well ...”
    "And he has his kinks, like any man, but if something brings him pleasure, if something excites him so much that it makes him cum, then why wouldn’t I want to give him that gift?”
    "He has kinks?”
    "Sure—who doesn’t?”
    "What sort of kinks?”
    "When he shoots off in my mouth, for example, he doesn’t like me to swallow all at once.  He likes me to hold his fuck on my tongue and salivate over it.  Then he grabs me by the jaw and opens my mouth so he can feed me the spit he’d been collecting as he fucked me.  He spits in my mouth and then deep kisses me, stirring together his cum and our respective spit with his tongue.  He likes to taste his own mancream in my mouth, and he gets off on me drinking a mixture of two juices.  When he lets me to swallow, he grabs my throat so he can feel his cum and spit go down.  But that’s just one of his many kinks.”
    "Do you suck him off a lot?”
    "Quite a lot!  How often is too often for a man to need his dick sucked?  I’ve surely swallowed my own body weight in his sperm.  And then there’s his piss—I actually wonder how many barrels-full of his piss I’ve guzzled.”
    "Sure—there are entire days when I drink nothing but his piss.  We both get off on the idea that it’s his piss flowing from my dick.  I’ve been piss-drunk off his cock more times than I can count over the years.”
    "Years of this?”
    "What did you think?  We played doctor as children and then kept playing doctor as we got bigger.  Why would we ever have stopped?”
    "How about when you started feeling attracted to other people?”
    "Sure, we both found ourselves attracted to other guys, and we both have relationships, like my relationship with you.  But other relationships have no bearing on our own brotherly bond.”
    "But when you fuck with your brother, you’re cheating on me.”
    "It couldn’t be further from cheating.  My brother and I have the same blood—we’re like one man.  He’s not some unknown entity.  You wouldn’t prefer that he go out prowling for mansex with strangers, would you?”
    I obviously never even thought about it!”
    "If he needs sexual relief, there’s no man who could fulfill it better than I.  Expect, perhaps, you.  Would you be second on his list, for the rare occasions I can’t be there for him?”
    "Are you seriously asking me ...”
    "I wouldn’t joke about something like that!  You can make out with him any way you like, but there are certain things you’ll want to do to ensure that he cums as powerfully as possible.”
    "Yeah, but ...”
    "Be sure to work his chest with your hands as you suck his cock.  One hand should concentrate on his right tit—that’s his more sensitive tit.  Stroke it and tickle it, but don’t pinch it too hard.  With your other hand, play with his fur on his chest like you’re petting a tomcat.  He totally gets off on feeling his chest hair fondled.  Come up for air now and then and be sure to slather his belly fur with your tongue.  You can’t make it too wet—he loves to be bathed in spit.  Then clean his entire chest with your tongue, paying special attention to his armpits.  You can spend several minutes licking each pit clean and he’ll never tire of it—especially if your chin is nice and stubbly for him.”
    "Yes, but ...”
    "The more thoroughly you lick on his armpits, the harder his cock will throb.  Believe me—all your tongue work will pay off when you trigger his load.  Oh, while you lick his chest and armpits, reach down and fondle between his balls and ass.  He’s real furry down there and likes to feel it played with.  You can tug on his balls a little, but he’s not into pain.  You can also finger his hole if you want.  He enjoys it, though it’s not crucial to his orgasm.”
    "Okay, but ...”
    "If you’ve got him really turned on, he’ll ask you to hold his fuckload in your mouth while he sucks you off, and then he’ll feed you back your own cum to mix with his own.  It’s true sexual alchemy, with your mouth serving as a retort of sorts, intermingling the sperm and spit of two men.”
    "Okay, you actually have me intrigued.  But I can’t picture actually having sex with your brother in your absence.  Don’t you guys do threeways?”
    "Never!  No—it’s just him and me.  Or you and me.  Or it could be him and you.  But if he and I are together, we’re not interested in anyone else.  Nothing personal.”
    "No offense taken ... I think.”

(Here the iPhone recording app ran out of space.)