Dumper sent me a Happy Birthday text and now his current gf stalks me

It’s been almost a year since my ex broke up with me. At the time, it was a complete blindside. He randomly called one day to tell me he fell out of love and couldn’t get out of the relationship fast enough. I later found out he’d been cheating/trying to cheat on me. He got into another relationship within 2 weeks of the break up

I was beyond pissed and disappointed. I didn’t know what I had done to deserve such a betrayal. I could see them all happy together on social media.

Now, it was my birthday a couple of days ago. As it turns out, it was his current gf’s birthday as well! She’s also in the same profession as me and posts similar content (music) on Instagram like I do.

He texted me after a year of silence. I only replied with a thank you. He proceeded to ask me a bunch of questions, hoping to catch up about my life. I never asked him anything back because I didn’t want to show any interest. He asked if I was in a relationship and I said no (I’m not ashamed of my choice)

After that day his gf has been stalking my social media accounts. I don’t think she knows I know about her. I have no idea why she suddenly started stalking me.

I take this as a sort of confirmation that my ex is not happy in the relationship because who tf texts their ex on their current gf’s birthday? And makes small talk only to ask if I’m single? I also know he’s been talking to people who put “suggestive” content on Instagram so there’s that too. But what do I make of all of this?

Tl;dr Ex left me for someone else, came back to wish me on my birthday and now his gf is stalking me for some reason.