What am I supposed to do to save myself from the trouble?

TLDR at the end is given. I have this guy friend who was friends with me since elementary school. We were just good friends and since I knew him ever since I was like 4 and till now, I never doubted him or felt that he would be romantically attracted to me. Everything was going well, until a week back, he did a dramatic proposal in front of everyone which threw me off guard. Like I literally turned back to see if I am standing between him and the girl he is proposing. That's how shocked I was. I never saw that coming since he never crossed his limits nor I noticed any explicit change in his behaviour. I rejected it as politely as I could. Initially I thought of accepting it and denying it later to avoid him the embarassment but few of my college friends were there and I don't want them to spread rumours about us since everyone around me including my family knows that he is just a friend. But this guy wouldn't listen. Initially he started to beg and now mentally harassing me by staring at me without any hesitation to the point my other friends left me alone to avoid the trouble. Creating a false rumour in college that I had sex with him by asking in front of everyone whether I got my periods on time mockingly and other inappropriate questions. I obviously tried to explain to others but they all laughed it off and left the place. I could stack the mental torture he is giving one after another. I don't even remember hugging him and he kinda made the college believe that I slept with him. When I asked why, he said it is just to make sure that I don't date anyone else than him. He is saying that all these years he was behind me only to get rejected. It's not like I asked him not to date anyone. In fact, we both are studious and never talked about these stuffs and only limited ourselves to academics and gossips about fellow students and teachers like girl besties. You all might suggest me to complain about him to college administration but it's not as easy as it is said. I have a good reputation in college. Every professor likes me because I study well and volunteer to help them. Getting my name spoiled this way hurts like hell. It's my first nightmare. On top of that, I wonder how supportive My family will be. They probably would say screw childhood friend. It's your mistake to trust a guy and you brought this to yourself. I am pretty sure this would be their reaction. TLDR : Mentally being harassed by a childhood friend to accept his love proposal.