My(23F) boyfriend(24M) of 5 years wants to fight in the war overseas. How should I approach this?

I'm from Ukraine and my bf is from Poland. He's been training for this for a long time. He feels lost and wants some hardcore action which he unfortunately won't be able to get where he lives. He wasn't like this in the beginning but the last 1.5 years he started this training and is now very serious about it. I tried talking to him about it and he just says he really needs to do this. Meanwhile I'm left alone here without anyone. Any advice?