What to do??? Please help

Ok I’m in a relationship and I have a child from a previous relationship, and I honestly don’t want anymore kids but my current bf kinda wants a child of his own even though the chances of him having a child are slim to none because when he was younger he had a surgery that prevents him from producing a lot of sperm but it’s still possible he could reproduce, and I’m actually scared he’s 53 and doesn’t have any kids so he kinda tries to get me pregnant but I have empathy for him and I told him that if it just so happens that I get pregnant I would love to have his child but in actuality I really don’t want to have anything child, I just don’t want to hurt his feelings, what should I do? Should I secretly get on birth control? Cause I know I can’t be taking plan b’s every single time, I really love him but it’s hard for me to tell him that I don’t want another child even tho the chances of him getting me pregnant are slim but it still could happen