I'd like to add my two cents in this. It seems you tried to cope with the impending divorce with your stbxw by filling that void, that need for intimate and personal connection. You likely missed the feeling you had with your wife and the closeness and projected these feelings and desires into another person, she likely did the same with you, sort of testing the waters. You probably have not fully healed from the hurt of your marriage and haven't looked inward and put in as much work as possible into your own self building and reflecting on who you are as a person. Think of it this way imagine your wife doing the same thing and bonding/connecting with a new person, this is purely coping and trying to remove a piece from the puzzle that is you and your identity and slotting a new puzzle piece hoping it fits perfectly and keeps the puzzle intact as if it was never broken or scrambled in the first place. While the feelings and connection made you feel alive again, this was a temporary fix, like putting duct tape on a broken bumper of your car hoping the car stays intact and whole.

Sometimes in these situations it's best to build the puzzle from the ground up and start with the pieces that are the most important, and when you are ready to finish the puzzle put in the pieces that complete your life puzzle only if they fit correctly.

I too thought going on dating apps and trying to connect with someone new in the immediate aftermath would bring me happiness and although many people will casually say you'll find someone new, you're still young, there's plenty of fish in the sea, etc. The truth is life and desires, emotions and personal relationships are much more complex than that. You need to start from the ground up and develop ways to find long term solutions for what you want your life to be, whether you still have hope of your ex or with someone new. Never has God given us such a glaring and obvious opportunity to look inward and improve ourselves and try to fix what is lacking in our character and work on truly finding out what we want of ourselves and from our life.
Once we have done this hard work only then can we truly move on, in one direction or another. I know all this sounds cliche but the road we travel to reach our destination is not always best approached with shortcuts, we are only cheating ourselves and delaying the journey by adding obstacles

Good luck in whatever path you choose