I'm going to break up with my boyfriend over text
Why do you want to break up with him in the first place?
He always drinks. If he was sober I wouldn't even consider this.
Your reason for breaking up with  your bf is totally justifiable. if you want to get out of your relationship you should tell that your bf in person. It's rude to break up over the text.
I just don't think it's worth speaking to him. I want a clean break.
You just said that if he were sober you wouldn't break up with him so that means he does have a chance to redeem himself. But aside from that just breaking up with him with a text message is rude and will leave him confused and just trying to find ways to contact you. If you really want a clean break, you will tell him directly so that he can understand and give you both closure.