Sex without love

Yesterday was the first time I had sex with someone new, it’s been about 4 months since me and my ex broke up we were together for about 2 years. We were each others first in everything. I don’t plan to date this new guy we just talk (he is aware I don’t want nothing serious at the moment just going with the flow) and have sex and a part of me feels so guilty for doing it like I owe my ex something. I find my self comparing my ex to this new guy in many aspects. His reactions to certain things I would say and do, my quirks, his affection. The sex was so different it was good but i felt no passion or desire. His kisses and touch hit differently . I cry just thinking about my ex, what we could of been, what we planned to be and how it all fell apart. Leaving for college eased the pain of not having to see him, I haven’t seen him since actually. I don’t know what to do a part of me wants to run back to him but the other doesn’t because of the reasons we broke up in the first place I feel like are still there. But man do I still love him. What do I do? Can anyone else relate? How do I get over him, I just want to stop feeling such guilt I want to move on.