Should I or Shouldn't i!?! What signs should I look for? Gentelmen, Help!

First question, and please forgive my english ;)
Well, I think you are doing well, you have to know which kind of guy hi is with girls (I mean, a real one-woman guy, a flirter, a flower-to-flower. ). The best way to know this is to asking your sister, but, does she now?
An important sign is that he has offered himself to pretend being your boyfriend. Almost all of us have tried this with girls we like. It doesn't always mean that, but it is almost never just a "friend offering with no more intentions".
Pay attention at how he looks other girls and how he looks at you. We all look at girls if they're pretty, and usually it is easy to find if we find them nice. To know If a guy likes you can be really easy:
First take a look at how he watches girls, he can be one of the straight guys that look without any hiding (or even lustfully), or maybe he is one of these shy guys that die of shame when caught looking.
Once you have an idea about how "coward" or "valiant" he is when looking at girls, try to find if he looks at you (and how he does it). Looks difficult, but here's a secret: my girl loves to find me watching, so she does this trick of going down to tie her shoes, or start doing something like brushing her hair or looking at herself in a pocket mirror. Anywhere he is around, he will look at you, maybe your hair, maybe your back, maybe your hands. You can act totally absorbed by what you are doing, and he will believe it and "relax" down. If he wants to look, he will do it now.
I said you need to now how he looks at other girls because it will help you find out what does mean how he looked at you.
Out of this "looking" thing, I can tell you we are easier to catch that girls are. Just be as pretty and sexy as you use to be and it won't be hard to find out what he thinks of you.

It sounds to me like he likes you in a 'more than a friend' type way. The problem is that you have a good relationship as friends, and he doesn't want to jeopardize that. He would rather have you as a friend and hide his feelings than risk everything and loose you from his life. He won't make a move until he is sure that it is what you want. That is the problem with nice guys, they won't risk upsetting you if they have read the signs wrong, by making a clumsy lunge for you. I think it is going to take you being just a little bit more daring, and letting him know that it is a two way attraction. Maybe by just something simple as giving him a kiss goodnight (on the cheek) something that is more flirtatious but can still be friendly. Take it from a nice guy that has been on the other side, we are really bad at reading the signs, so it will need to be a clear signal, in order for it to progress. Best of luck.