Sex with an ex.

Jay
So, my boyfriend and I broke up around 3 weeks ago. And we used to have sex a fair bit while we were in a relationship. I am really missing the sex that we used to have. 
He's the first guy that's ever made me come, and the sex was just great with him. 
Because I'm really missing the sex I'm considering sleeping with someone else. But then I'm also worried that I will later regret it and all that. 
Just wondering what everyone's opinions are?
Sleep with someone else or wait till I get into something serious with another person.