shy
Getting nervous easily around new people, especially those of your sexual preference. And although many people will claim blushing is a part of shyness too, this is not always the case. Many guys find this attractive in girls, although shy guys have a reputation for being ridiculed by girls.  
That person is shy, and usually backs away from meeting new people.

Ethan: So Max, are you going to ask Kelsey to the dance?
Max: Nah, I'm too shy.
Ethan: Come on, man, girls don't like shy guys, just be outgoing instead and it'll be easy!
Max: ... It's much easier to talk the talk than to walk the walk.