A 30-something year old guy and mets this girl about two and a half years ago. They are now best friends. He has always been sexually attracted to her, and would like to see if things could go to the next level. They kissed once about a year ago, which led to a talk where she said she didn't want to ruin their friendship.
He has never really had a close girl friend before, and definitely not one that he hasn't screwed around with. He comes to me wondering how can he go about seeing if this could work without compromising their friendship? Are there clues he can look for to see if she has some romantic interest in him?
Let's see, are there any clues? What about:
Clue #1: She told you she wasn't into it.
Clue #2: You're in the friend zone.
Clue #3: She's not sitting naked in your lap as you read this.
When someone wants to jump your bones, especially someone you hang out with all the time, the air gets so thick you could stuff a mattress with it. Therefore, if your friend does indeed want you, she knows all she has to do is reach out and grab it. Which she hasn't done. Clue #4.
Considering your difficulty befriending women without throwing it in them, I think this could be a positive experience for you. Being friends with the opposite sex is a very rewarding and educational experience. In your case, you could learn about the very different way the female mind works, get an honest, trusted, female point of view on things like dating and facial hair, and sometimes even catch a glimpse down her shirt when she bends over to pick her purse up of the floor.

You have all the clues you need, you just need to decide if it'll be too painful to hang around and watch her date other guys. If you can put your feelings aside, you may be pleasantly surprised at what great friends men and women can make. Especially men and women who've stuck by each other for two and a half years.