If they no longer want to associate with you because you aren't going to church every Sunday, that is just sad. If that isn't the case, then the most you need to tell them is that you aren't going on Sundays anymore. Family is family, and friends are friends. Religion may be how you met them, or a topic of conversation once in a while, but I don't see how your change in beliefs means they can no longer interact with you. As for your family, the best way to break it to them is to have them come to realise it on their own. If you simply stop going to church, and don't put on any sort of act that you are still Christian, they will gradually learn that your beliefs have changed, and when they finally realise the full truth, the blow will not be such a shock.
I would say don't lie to anyone about it, or put on any sort of act. At the same time, do not bring attention to the fact that you have lost that belief. They will come to the conclusion on their own, in a much less shocking way than you "coming clean" all of a sudden.
As far as your own feelings, you go with what you believe, and you will actually learn that though your church did teach you most of your moral lessons, you would have learned them anyway, without the church. Just because you don't read these moral lessons in the BIBLE doesn't mean that you won't find the same moral lessons elsewhere such as regular books, quality film, and simply life experiences. If someone does something to you that really sucks, you learn not to do it to someone else out of not wanting to make them feel as you felt. Just keep your eyes open to the world around you and the moral lessons will come from the most unexpected places. If it feels wrong to do it, simply don't do it
