What should i do?My dad wants me to marry someone from the family... But i already am in love with someone?

and we would love to get married. My father called me last night and told mer about the person he wants me to marry and he said if i won't agree he will be mad at me 4 ever. I cant make him mad but i dont want to be misreble.. i don't know what to do..Should i tell my father about him and try to work it out? or just listen to my father and make my family happy?