You added Cousin 1 as a friend on FB and you two have had some contact, you have common interest so inchalla you will eventually become proper friends.
I assumed that you just added him without any thought, but then again, I hope that you added him knowing that he was family - that is unlikely but I can always hope!!
For now it is good to see that you both are interacting with each other and for now that is great for me, it is a baby step in the right direction. Just knowing that you have some contact with your family is so great, even if you don't realise. I just hope you can forgive both Cousin 1 and me when the penny drops.
As they say patience is a virtue, so I have decided that I will not try to contact you or your (adoptive) parents until after your next birthday. That way, if you know and you added your cousin cause he is family, it will give you a chance to get to "know" The Family a bit through him. I'm sure he want to tell you he is your cousin but he has promised not do that. I have asked him to only respond you your direct questions if there ever are any, but as I said, I have assumed, that you just did the normal teenage thing of adding him without any questions.
I'm going back up North again next month and is looking forward to seeing The Family again. You never know you and your cousin might be chatting by then.