I think we are missing a LOT of information here. When did you decide to paint your room? Is it in the same house or building where you boyfriend lives? Was the project your idea? Did you ask him how to go about painting the room? Did he tell you, essentially, "Here's what you need to do: decide on a color you like; decide on the kind of finish you want (satin, flat, sheen, etc.); decide on how much you want to spend on paint and buy a pain in that price range; buy brushes and rollers and paint buckets, etc.?" Did he offer to go with you when you picked out the paint? Is this project something you've been telling him something like, "I want to repaint my room. I want it to look ___(whatever)____. I have time next week, so I can do it then. But I don't know how to do it. What do I need to do to repaint my room?"
It seems to me something like--not exactly, but something along the lines of-- the above conversation must have taken place, because you said he thinks he's done enough by "telling [you] what to do." So he had to have been asked, "What do I do?" and he has to have given you help in figuring out what you needed to do to complete YOUR project of repainting your room.
Also, there's a big difference between giving a neighbor a ride to the garage to pick up her car and helping her paint her house, for example. One is just a "neighborly thing to do," while the other requires a commitment of time and effort far beyond offering "a helping hand." Now if he had gone over to fix her plumbing or help her remodel her garage into a spare bedroom, then I'd say you have every reason to complain. But you are suggesting he should have told her, "Hey, it's YOUR car. Don't ask ME to get you to the garage. Walk. It's only four miles."
You're upset. I get it. But we're not getting the whole story. I am NOT saying he's "right" in telling you no, but I'm not ready to condemn him based on the version of the story you have given us.