yes
i spent £90 on my ex and got dumped a week later
Spend way more on your mom then your boyfriend
$10 - $20
For what? a birthday present? braces? food? clothing?
A card would be appropriate. A present would entail too much investment for you and perhaps too much obligation from him. Keep it simple, if you wish to acknowledge his birthday.
If you have asked him why he doesn't get you things. sometimes people have different cultures and don't think they have to. If it means that much to you, ask him and tell him that it is upsetting you.
There is no answer to that. It depends on what you buy. You could get something very cheap or something really extravagant and expensive. You may be able to afford a certain amount or you may want to spend different amounts of money depending on whose birthday it is or if it is a special age birthday.
a lot
a million
He probably doesn't have that much time to be with his girlfriend.
you really can spend all the time you want
It depends on how much you want to spend. If you're looking to spend a lot, I'm sure she'd love an ipod touch, or maybe an expensive bag or pair of shoes. If you want to spend less, try perfume, clothes or jewellery.
If you have 30 pounds, you are free to spend it as you wish. If you don't have 30 pounds, chances are your parents would not want to give you that much to spend on a friend's birthday, unless they are rich.