What is the meaning of がな at the end of the following sentence? (I divided it into 3 pieces because this is how it's written on the manga page it is taken from. Source: https://i.stack.imgur.com/vSnlY.jpg)
"齋藤仁【さいとうじん】"がそういうんじゃねえってことくらいは // ずっと見続けてきてんだわかる // 口では絶対【ぜって】ェ言ってやんねえがな
I read on dictionaries that がな can indicate a wish, or uncertainty, but I think it has just an emphatic value in this case. My attempt:
"Jin Saito" is not what he looks like / I know it 'cause I've always watched him / (But?) There's no way I can say it
I would also be grateful if you could correct any error in my translation, thank you!