Little help?

Hey all. So this is the first time I’ve done this. My ex has been the only person I’ve ever been intimate with and ig that’s why it’s so easy to just go and have sex. He had reached out wanting to see me and he seemed to excited, he was very sweet we hanged out and we’ve had sex a couple of times. But as the days passed, I’ve noticed that now he doesn’t want to see me as much and doesn’t even bother to text me. Now he ends up texting very late. I know we are not together so it’s not like he should be doing any of this. But this feels so weird to me, I’ve never done this before. I would love some advice as to why he’s acting like this…🥴