Because you didn’t state your needs, they may have assumed that you aren’t on the same page. So, instead of talking to you, they ignored you.
#3 They didn’t want anything serious. Now, I don’t want to assume, but I have a feeling that you slept with this person before making a commitment to each other. I’m not judging, we’ve all slept with people before even talking about what we want in relationships.
They didn’t want anything serious which is why they ignored you after sex. Depending on gender, men are able to have sex without feeling emotional, while women biologically have an emotional experience when having sex.
#4 It wasn’t “it.” Though everyone has sex, sexual experiences differ from person to person. For example, you may have amazing sex with one person while the next person you sleep with, the sex will be completely different. We’re not designed to have amazing sex with everyone we encounter. We all have different bodies. Each vagina and penis is different and not all of them will fit together.
#5 They freaked out. Listen, the sex was amazing, for you and your partner. It blew each other’s mind. But sex can be funny. You both had an amazing experience, but your partner is freaking out. They think about the future and what they should do which results in them freaking out and ignoring you.