Sleeping With A Guy To Early!?

Okay I really want to talk about this! So when I was like 15, I had a habit of falling in love to quick. So of course I ended up sleeping with a guy who promise he wouldn't leave me after we have sex, but after we completely stop talking I was shock. He told me a lie just to get in pants. So yeah, After that I always told myself that guys will say anything to get in your pants. But what made me mad is that my friend was dating for a couples weeks, so she slept with him, and he promise to stay with her after, and they been together for years now. How come that didnt happen to me. I also heard stories of people sleeping with their guy two weeks into the relationship, and they ended up staying together for years, and even getting married.

So my question is, can you sleep with a guy too early in the relationship and still be together?
or
When is it too early to sleep with a guy?

lol this been trap in my mind all day.