ok so my new boyfriend asked me to become a couple yesterday when we were out and we had a great day out as a couple but he said that we should keep our relationship quite because we wanted to see why our friend that used to have feelings for me stopped talking to him as much. But anyway I don't know why we should keep it quite and why we haven't changed our fb relationship status. We have kissed and walked about holding hands and he had his arm around me. Also we are going to to 2 parties together in the next few weeks and away for a weekend but i don't get why he has told me to keep quite about it ? is he just wanting to take it slow ?
we are 17

I wouldn't let that go on for too long... if he still wants to keep it quiet after a week, you need to talk to him about that. Maybe he is concerned about hurting his friend's feelings? I don't think he wants to keep it slow, from what you said I can see you're relationship is not going slow at all. So the only explanation that makes sense is that he wants to spare his friend from being hurt.