This seems rather harsh. It is in the nature of youth to be a little foolhardy from time to time, but you have to start somewhere. Is you mother open to you calling this a lesson learned and to allow you to carry on your relationship in more mature fashion?

On the legal side I don't know what the law is in your region but in the UK you would not be committing an offence: The age of consent in England and Wales is 16 regardless of sexual orientation or gender, as specified by the Sexual Offences Act 2003. However, if person A is over the age of 18 and is in a position of trust to person B who is under the age of 18, it is illegal for A to engage in sexual activity with B.