The Fourth Commandment is the First Commandment in regards to our responsiblilities towards our neighbors.
You should listen to your parents and, as long as you are living under their roof you should do as they say. If the household doesn't need the money, then save it for future needs and don't even consider the funds available to give to your acquaintance.
The poor will always be around, your parents won't always be around. Finally, what "things" are you buying for this fellow? If these things aren't basic needs, i.e., he's actually undernourished because he has not way to buy food and can't even buy clothes from Goodwill, then he's simply a con man and is stealing your money.