So...
I mean, it appears to me that this guy gave you a very clear warning sign that he did not want you being personally friendly with one of his friends. Whether he told you the reason why or you found out of your own accord- you still knew why and to do so would be hurtful to him and challenge any trust that you two had managed to begin to develop between the two of you.

It sounds like a lot of the bizarre behavior he was displaying was a result of these deep seated fears that A- whoever he dates will cheat on him and B- they will cheat on him with his "friend" Darryl.

If my potential SO told me anything approaching what Sheldon said to you about not adding Daryll on FB, I would not ever go near the guy, answer calls or texts, likely block him on facebook as well if it became apparent that he was trying to get close to me. Because there is clear hurt there and a complexity in the situation that I may never be able to understand; possibly being friendly to someone I don't know does not trump respecting the feelings of someone I care about already.

This doesn't excuse the impulsive and judgemental and kind of ridiculous behavior of sheldon- the accusations and insults, but his behavior doesn't excuse your reaction either.

You wanted to know what you did, and it was probably that you took his irrational fear personally and perhaps reacted in a retaliatory fashion- by creating a clear connection with darryl- whether you were actively doing so or not.

My suggestion would be to cut contact with the whole lot of them and start fresh. It sounds like a really unhealthy social scene, to be honest.