I recently went out with a guy and we really clicked. The thing is we had sex on the first date, anyway he was still very okay with me, but when I told him to meet again he said he had family problems. A couple of days passed and he was going to the clubs and asked me if I wanted to join and I went. And again he was really sweet that night buying me things and all. Nothing happened that night and he asked me to meet that week. The next day I told him when we could meet and he said we would see. And I told him that I didn't understand how one minute he would be okay and the next he would become indifferent. He didn't reply and he replied the day after saying he didn't want a relationship. I told him he was the one who said who wanted a relationship when we met not me. I had told him on the day we went out that it was fine for me if we just had sex, and he said we should remain fwb or just friends. Outline all the mistakes in what I did and add opinion on what I should have done or do. I work with this guy so I can't really escape him.

What happens if you get pregnant... because that can happen despite every precaution you take to prevent it.

What happens if he gives you something you can't clear up with a shot... like HPV, Herpes or AIDS.

40 years ago all you had to worry about was a baby, Syphillis or Ghonoreaha...

What is done is done... you can't change the past... you can and SHOULD prevent any future occurrences... if for no other reason than you work with him... that can turn ugly in an instant... and cost you both your jobs... I've seen it many times.
I'm no prude and like sex as much if not more than the next guy... but in this day and age casual sex is a very dangerous game to play.

You got what you wanted, sex. What else do you want and what's the confusion about? He changed his mind about the relationship. Nothing confusing about that either.

I had told him on the day we went out that it was fine for me if we just had sex

This says it all. It was fine with you if you just had sex, you told him that right away, and then you expected a relationship? Not going to happen.

He got what he wanted, you got what you wanted, the end.

If you want a relationship, don't be so eager to jump in the sack, and definitely don't tell the guy that it's okay if you just have sex, nothing more. Unless that's all you want.