(36F) How do I break it off with a guy (40M) I have been seeing for a couple months without losing his friendship?

I have been dating/seeing this fellow for a couple of months. I was somewhat pursuing him, but have given up on him after the relationship hasn't progressed forward much. He is very private and seems to keep me separate from his life. I haven't pushed it, but started backing away when I noticed that I was pursuing him. A month ago, I met someone that I really like and would enjoy seeing him more. The relationship with the new guy isn't exclusive, but I just realized that I am done with the other guy. My question is: How do I break him off without losing our friendship? We were pretty good friends before we got involved (sexually) and he stated in the past that he likes to remain friends with ex's. I have barely talked to him in the past couple of weeks and haven't met up with him in person (my choice)....

tl;dr: Been dating M for a couple months. Relationship hasn't advanced. I want to end the relationship, but still remain friends. How do I break it off so that I can be friends?