When I separated from my AH, it really helped me to go no contact. It was the only way for me to really focus on myself and figure out what it is that I want.
But if that is not something you want to do, then maybe you should just tell him what you told us. I.e. you could tell him that you love him and that you're happy to continue talking to him about how his day is going etc. but that you don't want to discuss xyz. Put a boundary into place, such as if he does talk about xyz, you can remind him not to talk about it and if he continues you tell him that you will need to hang up. Your boundary doesn't have to look exactly like what I described... just make it something that works for you and make sure you follow through when he oversteps (that's the most important aspect of any boundary and something I am still struggling with).
I wish you all the best. Take the time to really care for yourself and stay strong!