AIBU to be upset about my partner talking to his ex??

[Babewiththepower0]

Hi so a bit of background, when me and my partner first got together 7 years ago his ex tried to get between us and was trying to turn family members against me. They had been split up for about 2 years before we got together. 5 months into our relationship I was fed up of her trying to break us up and find out information about our relationship from His family and telling lies about me, (my partner had talked to her and asked her to stop several times) I told him that I couldn't be with him like this so he decided to cut her out of his life.

Background on them she cheated on him a number of times, was a horrible person to him, he lost all his friends while they were together, and he ended the relationship (they were together about 4/5years)

So today this ex has messaged my partner out of the blue saying the pet they had when they were together had passed away. He was obviously upset and I tried to comfort him. He told me he wanted to call her just to ask about what happened etc to the pet. I was hesitant but I was like if you need closure then fine. He phones her and is on the phone for like 40mins I can overhear and most of the convo isn't about the pet. Then I see messages from her basically saying if I have a problem with them talking it's my problem and that she liked catching up, him telling her she's awesome and that sort of thing. The random times she pops up in conversation normally he says she's a horrible person (in much stronger words). I'm hurt that he lied to me as he said they had only discussed the pet over phone and video chat but I know that's not true and he said that the messages were the same but they'd been reminiscing and talking about me. AIBU? I feel likes he's opening us up to trouble all over again even though she has a partner, everything about their conversation was flirty thanks for reading if you made it this far, he doesn't see why I would be upset.