You’re overthinking this way too much.
While reading, my first thought was that if he was interested, he would have done something about it already. Your excuse was that your ex was around so he couldn’t. That doesn’t hold water. He can get a hold of you and ask you out other ways, like social media or getting your number.
Honestly, as List and Anon said, I’d take a more direct approach.
But before you do that, you need to decide how’d you want something to go down, as Kate mentioned, then proceed accordingly.
You’re acting like a high schooler right now.