What to do..???

Hello everyone...i really need your help.I am a student and for me my friends are my life.I have two best friends.Both of them are very close to me.They are like my family.Actually problem started when one of my best friend proposed me.In the beginning i took it as a joke but later on i came to know that he is very serious about me.I said no to him because i was not ready for any relationship.But after few days he started hurting himself so for him i said yes.I didn't tell my another bestie about our relationship because i don't want to hurt him.But one day he came to know about our relationship and he stopped talking to me.He said that he also loves me and he cannot see me with someone else.I tried to make him understand but he is not ready to listen anything.This thing is really hurting me.I don't want him to go.Why can't we be friends like before?Why he is behaving like this?