Disclaimer: I'm not saying hes right, im just offering a possible answer to your question. You asked "what do I do" but before that you're probably wondering, "what is he thinking?"

it's possible at his age, he's selfish and wasn't impressed with the sex. Of course, it's your first time! And being selfish he's acting aloof.

So 2 things are happening concurrently - he's acting aloof and you're hurt.

You should talk to him about it, and ask him why he wasn't there for you and get his take.

Everyone is saying he's not good or your should break up but relationships don't work like that. Reddit forums are so black and white bc people who post don't have to live with the consequences of YOUR decision. YOUR being the key word.

When considering a breakup or a bad girl/boyfriend I always ask the following questions:

1. Is the person aware of how they hurt you
2. Is the person willing to change once they are aware
3. Are they capable of changing
4. Can they stick with the discipline that change requires

The previous "blaming" and walking away while you cried are 2 pretty big red flags, but if you love them maybe a final conversation is worth it. If you can get what he's thinking then you can know for sure he's a huge jerk and leave with a clear mind and heart.

Hope this helps.