Bad sex experiences happen. Just as bad experiences happen in every other part of life. But when we fall off our bike, we get back up. If at first you don’t succeed, try and try again, right?
Sex is amazing. Anal is amazing. And he really shouldn’t need persuading, but everyone is allowed to have likes and dislikes. Has your boyfriend shared his bad experience with you? Knowing what he didn’t like might assist you in “persuading.”
You two are naked together and you’re sexing on the regular - there’s no reason why the two of you should shy away from honest conversation. Did it hurt him? Was there poop? There are solutions to both - Slow with lube and timing; It’s a cleaner experience if you’ve been empty and clean for a few hours before.
Talk to him and tell him how much you like it. Ask HIM how you can persuade him!