Think of it not as a debate, but an opportunity to be calm but sturdy in witnessing to him… don’t give up on yourself nor this person. It’s his soul that is thirsting/searching under the surface for answers about God in a sense for a reason- why else would he be confronting you?. I truly believe there is something hidden within this person’s soul that just needs some consolation about Catholicism in simpler terms (perhaps) for this person to comprehend the goodness & prosperity of our faith. In my experiences with Protestants questioning Catholic teachings & my faith, they would try getting under my skin to share their misunderstandings of particular concepts- but I didn’t let them bother me most of the time. Guard your words & actions with humility and patience in Christ, otherwise this person will assume all Catholics are like you…don’t let this person’s opinion of you matter because God alone is enough. Most importantly, pray for this person’s heart, mind, & soul to draw closer to Christ and be open to exploring Catholicism truly for what it is without judgement. With God the Father, God the Son, & God the Holy Spirit- you can do this. I will pray for this person wherever he or she is at along his/her faith journey & that he/she finds Christ because there’s no greater adventure, seeks Christ for there’s no greater achievement, & learns to truly love Christ for there’s no greater love than to be loved by Christ Himself. Hope that helps a bit.