Is it mandatory to marry a girl with whome you had sex with

I'm 20 year old of a Muslim guy living in Hyderabad. I was in a relationship with a 19 year old Muslim girl for 8 months. In the 2nd month itself we had confessed about our relation to our respective parents. And my parents refused to this relationship but still the girl's father gave me 2 years of time to convince my parents and get me married to his daughter. We continued to stay in contact and in the 4th month we got physical and had sex for 3-4 times knowing the fact that nothing has been fixed/known about where we are going to end up, Whether we would get married or not, We both knew that Recently, my parents had a talk to the girl's family and refused for this relationship and adviced them to move on. But the girl confessed to her family that we had physical relationship and had sex many times. Now the girl's family is saying that I cannot leave her like this after having sex with the girl, that it will spoil her life. And if I leave her, they won't sit quite about it What are the possibilities now, how had of a condition I'm stuck into? Do I still have to marry her? Or I can just walk off saying that "it was a mutual decision and we both knew we may or may not get married and now we cannot get married because I dont want to marry her nor I parents want me to marry a girl like her" Note: She is not pregnant, We had save sex I don't want this relationship anymore it is impossible for me to get married at such an early age due to and educational problems