Taurus was the other man

So, for a while there was this Taurus man with an aquarius moon that I used to hang out with. I thought we were just friends, but eventually there was a slip up and we had sexual relations. It was a one time thing, and it was a massive mistake.I mean, I never really thought he liked me to begin with because he would always disappear for 2 weeks and then pop up again, and then he would barely text me. He would also try to go out to dinner with me and not call it a date.

Yesterday he saw a pisces guy on my snapchat story and tried to contact me, and talk to me, but I ignored him. Last night I posted a video saying I love you to the same pisces guy on snapchat. He put two and two together and realized I obviously had a bf. He asked me if I had been in a relationship when we had sexual relations, told me I had ruined his night, wished me well in life, and then said bye forever. But, he's still my friend on facebook, he's still my friend on snapchat, and I'm pretty sure my number is still saved t his phone.

But why is he acting this way if he was never really interested in me to begin with?

Of course pisces guy was aware of what was going on, I never keep anything from him.