Never know the right thing to say

I’ve started talking to my ex again about a month ago, he just got out of a long term relationship. We’ve had occasional flings and sometimes we talk when he’s feeling sad or depressed but I feel like I never know he right thing to say... I try to keep the conversation going at times and bring up different topics but maybe I’m trying too hard and our spark isn’t there anymore. I asked him about testing for stds and he got kinda offended and another time I mentioned how I didn’t cum and he got offended as well. He causes more frustration than joy and I’ve been telling myself to cut him off and move on to someone new who will give me more than what he gives me but I can’t seem to let him go. I lost contact with him for 3 years and we’ve both clearly changed. I feel so bad and I feel like a have a runny mouth. I try so hard not to sound mean but I guess it’s not working. Any tips for my current situation and how to be mindful about what I say?