1) men are sometimes (often) creepy when they're alone with you socially, especially for the first time. There are many, many men I've met who are ok in the office/classroom but lose all sense once outside it: they seem to think that once you're on a date, you've scored and can "let loose". A tagalong friend is the easiest way to make sure they don't turn embarrassing or annoying too quickly, and a way to cool them off. Only if you can pass a friend date can you hope to pass a real date.
2) the woman wants to be friends, so saying "get away from me, I will never find you sexually appealing" is off the table. This is a negotiation: you ask "can we go on a dte", she responds "I will only settle for a social date". The non-nerd response is either to switch off your libido and go along with it, or make an excuse and back out. If you're too stupid to get out of the lunch date with Bob the One Musketeer, you deserve him. It will teach you humility.
3) the woman is as socially awkward as you, and doesn't realize this is a date and not a business/casual meeting. Yes, men have to put up with nerds, too.
The amount of sexist !$%*!$%* on this board is staggering.
Ok guys, don't give up hope if a girl invites her friends to an event you've asked her to. Mostly she is doing this because she is semi-interested, but she is nervous about spending time alone with you. You can't expect a girl to be your girlfriend over night. You have to build a relationship with a woman and make her feel comfortable, which takes a long time.