I just want to add to the "well, once you're older..." line of comments. I know you're not looking for such detailed responses when you're just venting, but maybe these comments will make sense to you -and maybe they will help some of the other younger guys here, who are struggling with similar worries.
Here is reality: Almost all of the friends you grow up with are not likely to be the friends you have once you're done with school, have left your hometown, or once people start hitting major adult life milestones at a different pace (serious relationships, having children, building career, etc.). I know this can be hard to believe, because your friendships seem so important now. They are. Now. That WILL change. It changes for everyone, trans or not.
Friendships are often a product of circumstances in general, and this is PARTICULARLY true of friends made before you have graduated and finished school. They are the people you have to spend time with in school, church, neighborhood, the kids of your parents' friends, in your dorm, in your college support group, etc. You have so much in common. You get used to each other. I'm not saying these aren't real friendships. Of course they are. However, they are friendships with very obvious life spans. They *will* expire as you grow up, and almost none of these people who have been important to you before will matter once your friendship takes actual work, rather than convenience.
Terry, you're a cool dude, and you're going to have plenty of friends. You will build close relationships with people who get you - for who you are - and you really won't miss any of the people who are dropping you because "oh no! Being trans is a sin!" As you focus on your future education/career plans, the serious relationships in your life (whether it's with your current gf or someone else), your hobbies that will be with you for your life (like biking), the church or place you like to worship and feel welcomed, etc, there just won't be the same space or interest in having people around who are not compatible with all that. You won't have time or interest in caring about someone who knew you way back when in bible college. And there WILL be people you befriend, just because you work together, ride together, they are friends of your girlfriend (or wife in future), etc.
As for family, well, that's different. It sounds like your Mom does support you, in her own way, and she'll continue to be there for you. Will your Dad come around? Maybe, maybe not. Hard to say. Will *YOU* reach a point where you don't need/want/care about what your Mom & Dad think to the same extent? Of course you will. You are still developing into a healthy, independent adult. Your parents will always be your parents, but most people don't spend their adult lives worried about the approval of their parents (and there is always therapy for those who do - heh).
I know that right NOW it doesn't help me to tell you or any of the other young guys, "These people won't matter to you in the future - at all or as much" when it comes to friends or family. But that's true for me, and it's true for almost everyone I know who is my age, whether they are trans or not. And it sounds like this is what the other guys here are saying too. Consider it our form of "It gets better" for those of you still struggling with how the people around you are handling your transition.