Hi, original poster. You don't need to worry about a therapist judging you or telling your family about sexuality. The only time a therapist might go to your family would be if you are presenting danger to yourself, such as if they think you might commit suicide. Then they would only tell your parents the things they needed to know to keep you safe. Something such as the fact that you have a girlfriend would be very unlikely to get back to your parents. Also, a therapist would know not to judge anybody. They are trained professionals who are there to be on your side and help you get better. There is absolutely no reason for you to be afraid of going to one.
Of course, you also don't have to mention your girlfriend when you are seeking out therapy. All you have to say if you are not comfortable telling people the rest is that you've been really depressed for a while. Tell your parents and they will get you the help you need. If you don't think they'll be supportive, then talk to a teacher or guidance counselor at your school that you trust.
I don't think I've ever heard the term ROCD before, and I've been reading a lot about relationships for the past 15 years or so. It's pretty normal to feel obsessive about somebody when you're falling for somebody. It feels good to dream about love, so almost everyone does it at some point. It can be problematic when you're using it to escape other problems in your life. Then the issue is that you're not taking care of the things that need to be done more than the romantic obsession. It's not something you should be beating yourself up for. You just need to start taking care of those things. You don't need to give up your relationship with your girlfriend. You can just start learning how to balance all of the areas in your life, which will better for both you and your relationship.
I think seeking out treatment for all of the other reasons you mentioned is a very good idea. I'm betting that you will see it's much better than you thought it would. If you don't like the first therapist you see, keep trying other ones until you find one you do like. Good luck!
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy