Consanguinous marriages, That is between first cousins ( as you and your Aunt's son are ) are known to cause many problems especially to the baby born. There are high chances of abnormalities and diseases due to close lineage.
Next Steps
You are just 19, and your decision could be a "infatuation". Please rethink. and If needed confide in your mother. If needed concentrate on studies and job and you can postpone your decision by few years till you find suitable match