Why is he so angry that I'm seeing someone? We never dated or even kissed?

[Anonymous]

But I did used to drop hints that I liked him and we would flirt a little

[TheLawfulGood]

There's a fair chance that he felt the flirting was leading up to something more. Generally, when guys even get flirting or hints from a girl, we ride that high for AGES. That's partially why it's so easy for guys to fall head over heels for a girl. I'm willing to bet he felt like you toyed with his emotions, even if you had no idea that's what was going on. It would really smooth things out if you sat down with him and talked it over; explain the misunderstanding, and let him know that mistakes were made on both sides. You can still be friends, you can still salvage this.