Yeah, I wouldn’t tell her about your ex. I feel like that’s unnecessary and would only hurt her worse. Just stick with the fact that you don’t see a future with her and you want to be alone.  And then make sure you stay single for a while afterwards without even dating around until you’re able to let go of your ex more and aren’t suffering over thoughts of her anymore. And like I said in the other post, you don’t have to let go of your ex 100% because I’m not even sure that’ll be possible until you find a better match for you, but you do have to get to the point where you are truly open to the fact that your ex may not be the best person for you… that there may be someone else out there and you’re truly open to meeting her.