What to do when they come back?

I am facing this right now and I am ecstatic to report that I finally have an answer that makes sense, after all of these years. Nothing. You do nothing. You do not even respond to the message in any way, shape, or form.
To clarify, my most recent qualifier (D. from Buffalo) has not come back. However, another man (R. from Buffalo) texted me today. I was seeing R at the same time I was seeing D. In all honesty, I was using R to try to distract myself from my cravings of D. I met R on Tinder and had one encounter with him. He and his family have a lot of money and he's a good looking guy. He was smart, successful, and seemed sweet as well. However, it was a sexual arrangement on both of our parts and when I started withdrawal on November 6, I stopped seeing R and D.
I last talked to R in January. In June, he texted me. I did not respond. And today he texted me again. I have not, nor will I, respond this time either. Obviously I do not know the guy well but I think he would be a reminder of the one that I really wanted, D. Moreover, I am content with my life being single. I enjoy my life and everyone in it and for the first time in my life, I am satisfied and in a great place. No man will ever ruin that for me again!