Be nice...not to be nice...?

Be nice and being used by others or be not so nice to avoid being used? In uni I'd learnt that...friendship isn't real anymore...not all like that but mostly. Probably that is why sometimes I think i'd used people too? But I don't feel good each time when that happens. I did it just to get even... I don't like to be used but sometimes I really treasure those "friends" so I'll just let it be. Perhaps its Mutualism relationship? Hrmmm...sometimes i just cant help it but to wonder do I have friends in uni?