First, lose the ring! In fact, sell it. I stopped wearing my rings as soon as it was clear the relationships were over. These were not acts of "single-hood" but rather acts of freedom. There is no stronger symbol of marriage than a ring. Set yourself free. I sold my wedding bands for 25% of what they cost but so what? They were symbols of the past and of failures and I don't need that in my life. As Jackson Browne wrote in his song "These Days," "Don't confront me with my failures, I have not forgotten them."
Second, I assume Trooper is your dog. You wrote, "Trooper seems to like people." There are lots and lots of other people for Trooper to be friendly with. As another poster wrote, you and your ex split for very good reasons. Try to remember them! Pets remember people who were kind to them but they don't know the complexities of your relationship with the ex. Trust me, there are lots of people for you to have meaningful relationships with, (not even necessarily romantic ones), and Trooper will like them, too.
Third, your ex may be trying to manipulate you by "making some good points." Remember that he knows your soft spots and buttons, just as you (consciously or not) know his. Don't let him put you in a position where you lose your independence: that's why you split in the first place!
Lastly, I strongly admire your desire to remember to not give your heart to anyone who doesn't deserve it. You might get hurt in a new relationship because letting go is part of falling in love. However, you already know how your ex has hurt you. Don't give him that power over you again because he's already proven he's unworthy of your trust.
In closing, I'm a romantic and I got married for the third time several months ago. My new wife has been a friend for 40 years and we were totally surprised when we started falling in love. One big reason we get along so well is that we already know one another's strengths and weaknesses; there weren't many surprises between us. Our mutual goal is to be straight up and honest with one another and that keeps the little things from escalating. As a result, we're having the times of our lives together! There's hope for happiness and I encourage you to be open to new adventures.