You have already talked too much, tell current boss goodbye, ask famous company when do you want me to start work . This is how life works, a real friend will tell you now is time to move up in the world.
Siam
I think it would be rude to hurt the friendship by just saying goodbye.
My boss thinks I can do better so he wants me to leave in 2019 anyway. I just don't want to go around interviewing before then, without telling my boss/friend.
I would tell him about it and I'm sure he will have a favorable response. Help him make a good transition and find someone to replace you.
Oh and it's non of the other company's business what you say between you and your friend. Don't tell them anything about it, it's not ok for them to even ask.