My jungler decided to go full damage when we needed a tank

I didn't mind at all, he was fed early and was doing well throughout the game. Later on however when we had to group he didn't do anything except kill the enemy adc who was already pretty worthless because she was doing really bad. Later on we lost and now I'm really sad we lost because our jungler who is a good player decided to build full AP, WHAT DO I DO!!?