Why would you care what your Mum, Dad or least of all her room mate thinks? If you fancy her and she is up for it, why not? Why would you be trying to determine if a relationship is serious or not before it starts? No relationship is 'serious' until it is. It may just be a shag (with protection obviously), who cares? Live your life freely whilst you are young and you can mate. You will have plenty of time for thinking about serious relationships before you know it, I assure you.