But he needs just one person who believes in him and I want to be that person, I'm just so worried that i might not be strong enough
The above statement is opinion, not fact. It's not your responsibility to believe in him. It's his. Recovery from alcoholism is hard work, and it's not something you can do for him, or even will for him. He has to want to do it, and if he ever chooses to do so, he will do it with or without you in his life. I'm not trying in any way to sound harsh, but the truth of the matter is that no one 'needs' anyone else to become sober. They just don't.