How can you tell when a guy just wants sex?

So I went out with this guy last week. We had a perfect date and I ended up sleeping with him.

Prior to our date he was texting me constantly, so flirtatious, and we had AMAZING chemistry. After the date though, he has barely texted me. He mentioned hanging out this weekend but I told him I’ll be out of town. Last night I texted him and he said he was gonna text me back in a few and I haven’t heard back.

I’m pretty sure he just wanted sex. Which is fine. But he literally took me on the most perfect and fun date which is very confusing. I just don’t get why he changed? He pulled away after sleeping with me for sure. Does it sound like he just wants sex?