Best friend or boyfriend?

Sometimes in life you need to take risks. This would be a good opportunity to go for all or nothing. Well, it seems like you have nothing to lose really. He knows you like him, and he's known you for quite a while (3 years?). He wouldn't end your friendship just because you officially told him how you feel. You'll actually be relieved once you get your feelings off your chest.

I suggest you go for it. Get him alone, in person, face to face and tell him how you feel. You have good intentions. You said you would do anything to make him happy and prevent girls from treating him badly, I wish my girlfriend would think like you! Anyways, the easiest way to tell him is to describe to him what you said in this question. Say something similar to your question, except put it in a verse to him.

Say things like "I've felt this way for 3 years, ever since I met you I've connected with you and I feel as if I can trust you with anything and be myself around you", so yeah not word for word but you get the point. Also add something about the fact that you rather see him happy than with the girls who treat him bad. I'm almost positive that your friendship won't end because of this question. 3 years of friendship lost over a question? If anything, this guy should be flattered by a girl asking him out. Just think positive and remember, be yourself.

Maybe he does think/ know you are being serious
but doesn't see you in that way
and so cover it up pretending that he thinks you are joking
i don't know properly, but maybe he sees you more like a sister as opposed to a girlfriend.
is it worth loosing your friendship over?

You should at least give it a try
tell him how you feel and that you would give anything to make him happy
if he won't take your feeling for him serious then is it worth stressing over?

This is way too cute! The same thing happened to me except backwards, my best friend was in love with me for a very long time. I know it's super intimidating telling someone how you feel...nobody wants to be rejected by a person they adore. If he does deny you (which I seriously doubt) at least you'll know that you did everything you could and you'll know it's not your fault that you're not together. Best friends make the best boyfriends/girlfriends and it's more special that way. Good luck. I wanna know what happens this brings back lots of memories