My DH used to chew. Had been for almost 10 yrs and considered himself a pretty heavy user. When I went in to my dr for a regular appt (when he was still chewing), I asked her about it. She said it 'could' effect it... there's nothing definite but some studies show it can. So, she said if after 6 months we weren't pregnant, she was going to order a SA. About a month or so before his SA appt, he quit out of the blue, cold turkey.. then got a bad SA. Dr ordered a second one + made him schedule a urologist appt. Second SA was 3+ months after quitting, so should've been well out of his system, no improvement.
So, who knows in our case. Maybe it would've been even worse if he hadn't quit?
I was very much urging him to quit - which wasn't good. As hard as it is for you, he needs to do it on his own. Because that will improve his success if he feels ready, not forced. Hopefully it will hit him one day & he'll surprise you!