"How does that make you feel?" isn't actually the cop-out it's sometimes made to be. A lot of the time, people don't really examine their emotions, and what's causing them, and why they're doing what they're doing. Simply by articulating what your emotions are, you're introducing an element of critical thinking. "I am feeling X. I have this feeling because he did Y, and that makes me want to respond with Z." It allows you to take a small step back and eye the situation more impassively, and hopefully give it a more critical eye. And - forgive me for saying so - it sounds like you probably could use more of this. 
We cannot control the emotions we feel, to a great extent. But we CAN control our actions. Getting angry when somebody cuts us off in traffic is a completely natural thing to happen, and nobody would blame anybody for feeling angry. But you WOULD be called to task if you then slammed your car into theirs. You couldn't simply tell the cops "hey, he cut me off, and I got angry". Your anger would be totally valid. Your actions - slamming into his car -would not be.
Similarly, when you had this rather tumultuous relationship with this guy, your emotions - anger, grief, confusion - were all totally valid. Your actions, in many cases, were not. It's totally understandable to feel upset, angry, heartbroken when a relationship ends badly. But your actions can't be waved away with "well, I was emotional". You do need to step back and - yes! - think about your emotions. "What am I feeling? Why am I feeling this way? What is this emotion making me want to do? What will be the ramifications if I do this thing? Will the net result be positive or negative? Will I actually come away from this action feeling better or worse about myself?"
There's a saying I like to throw around - "the best revenge is a life well-lived". It's pithy, but there's a lot of truth in those few words. 
* If you focus your time and energy in a "life well-lived", you will be focusing on things that make you happy, and put you in a better spot. That's a far better place to put your time and energy than in "checking out what the ex is up to".
* If by some chance your ex- DOES peek back to see what you're up to, you'll be in that better spot. 
* And if your ex- DOESN'T peek back to see what you're up to...well, you're busy living a damn good life. Who the hell cares if this guy from your past is watching or not? 
 
So if you want some advice on "what to do now"...
* Don't "end it" with this guy. Assume it's ALREADY ended. Delete the number from the phone and block it. Block him on social media. If he's not reachable on your phone or computer, you'll be a lot less tempted to look in on him, or to contact him. Act like he vanished into outer space, and you can never contact him again. Eyes forward.
* Whenever you feel the emotions swimming back, take that step back. Say it all out loud (scream it, or blubber it through the tears, if necessary). "I'm feeling X. I'm feeling this way because of Y. This feeling is making me want to do Z." Then, continue on from there. "What will the ramifications of this action be? Will this end up being a positive or negative thing? Will I feel better about myself and about the situation if I actually do that? What might be some other options I can do instead of this action, that might have a more positive outcome?"
* Related to that last bit...nature abhors a vacuum. You can't simply "not do" something - you'll be sitting there, sitting on your hands, itching to do SOMETHING. So, start coming up with some things to do. What are some things that make you happy? Make a list on your phone. Reading a good story? A hot bath? Jogging? Playing R&B hits on your kazoo? It really doesn't matter what the hell they are. Write as many down as you possibly can think of. Then, give yourself permission to go do these things next time you feel the urge to contact the guy. "Instead of contacting him, I'm going to go for a jog to help get into better shape." "Instead of getting angry about him again, I'm going to put on my favorite album, and draw pictures of angry koala bears." Whatever works best for you. 
 
Lex