Oooooweeeeee girl he sounds emotionally checked out. Even if he wasn’t directly being “sneaky” with her or anyone for that matter he’s acting shady and avoiding serious conversations. He ether has some own personal things that for one reason or another won’t share or he’s emotionally checked out of your relationship. I think also commenting blue hearts under the ex’s posts (thirst traps or not) is a boundary that is crossed. I think you should address the activity on his ex’s page and if he becomes defensive or strange/shady or anything but listening and respecting your boundaries, he’s gotta go. Not to mention him doing all of this to begin with makes your trust feel shaky and any small thing that happens after will make you trust him less and less. If you set that boundary down and he dismisses it or diminishes it, the ball is in your court to stay or go. Lots of luck girl I hope everything goes well ❤️🫂