Your particular brand of boyfriend is one of those who might not be so open to doing things he doesn't want to do, so instead of agreeing to do things that he will eventually end up doing with you, he just says "maybe" until he decides that its not worth it to not go with you because of the eventual discussion about why you never do things that you want to do.
Basically, he's a little bit selfish. If you want to know if he means "maybe" or "no" then just pay attention to what actually happens. Does he always eventually do what you asked? If so your issue is that he has to take so much time thinking about it, which would only be an issue if you're the type to agree to whatever your boyfriend wants to do because you're a chick and that's what chicks tend to do.
I'd suggest that you bring it up to him. Talk to him about it and how frustrating it makes you that he always hits you with the "maybe" and how it makes you feel like he doesn't want to do things with you. If he's a good guy, he'll listen and think about how he'd feel and then perhaps you will see some change.
Good luck.
ugh I feel ya I am in the same boat...I'm ok with them telling me no...i just hate this maybe crap...I never know whether to expect them or not -__-...girls are ok with no...but very good advice Panama...thanks!