You sound like a very good friend!

Why are your lightweight friends getting that drunk to begin with? They should slow down. Set aside sex for a second. Drinking yourself to the point of passing out puts you in serious risk of all kinds of health problems, especially if you do it regularly. Speaking as a male of above-average height and weight who loves drinking and sex, I can't imagine either being enjoyable to have that much booze. And even if it doesn't affect your medical condition, it damn well opens up a critical period of vulnerablility to to getting robbed or assaulted on the way home or at your front door, and that's true no matter who you are.

I'm pro-drinking and pro-sex.  Most Americans don't have enough of either. That said, the sex matter is very delicate, and drinking and sex only mix well when the drinking comes in small doses. Sometimes boundaries are really hard to set, even for sober adults. While that guy in your college who bragged was definitely a sack of shit, things often are a lot more vague when a horny, drunk male meets a horny-but-maybe-not-ready female whose judgment is compromised - and I'm sorry to say, even though no is no, it's also a lot harder to say it's rape if she goes to third base and wants to stop while he expects a home run.

Controlling booze intake, however, at least partially negates the issue of having to figure out whether it was rape or not the next morning.  Our bodies handle a few drinks well, but they don't take a pounding well. Drink slowly and stagger your drinks with tall glasses of water. Try to avoid so many shots. Shots contain similar amounts of alcohol to a glass of beer or wine, but you take them in faster and people often double and triple up. Try to make sure you had at least a moderate meal before going out. Personally, I try not to mix too many different drinks because it hits me harder, but maybe that's just me.

If you really do drink too much, make sure to take some vitamin B supplements, again with healthy amounts of water, to ward off a hangover. Vitamin B deficiency is a major cause of hangovers. I suggest a packet or two of high-quality brewing yeast (mixed with water), as suggested in Charlie Papazian's "The Joy of Homebrewing," but if you can't stomach that, I've had good experience with vitamin supplements too; Emergen-C is a good one that's usually readily available at convenience stores in big cities, but it's cheaper to have a box of it at home - http://www.emergenc.com/. As Papazian points out, drinking unfiltered (usually "craft") beers often lessens the effects of hangovers because, compared to major brands, craft beers still have healthy amounts of live or recently deceased, vitamin B-rich yeast cells in them. This may be true of wine too, so you might want to experiment a bit to see what drinks leave you feeling better.

You can drink (a lot), still have fun, but not completely compromise yourself cognitively and physically.  It's a happy medium. :-D