There is definitely irony in the second sentence. X is actually telling (s)he is (actually was) unaware of their relationship.

You didn’t? Well, that shows how much I’m aware of it! I was convinced you quarreled!

Dropping vous voyez would make the sentence less intelligible, a possible alternative might be:

Non ? Eh bien, je suis au courant maintenant ! J’étais persuadé que vous aviez eu des mots !

Here "Comme je suis [thing]" is "how [thing] I am". You can tell because of "tu as vu".

It also works with avoir :

Tu as vu comme j’ai progressé ? = Have you seen how much I’ve improved ?

It’s hard to translate "être au courant" in a short way so it looks similar in english. I’d say it’s something like :

"You see how aware I am of what’s happening between you two ? I was certain you argued !"

About your last part, using "comme" alone (in the beginning of a sentence) means you’re impressed by something, it’s an exclamation.

Comme c’est beau ! = It’s so beautiful !

A more casual say of saying is with "comment": "Comment j’ai faim !" = "Man, I’m hungry"

"Comme" can also express a cause, if it’s accompanied by the consequence.

Comme vous me dites jamais rien, je sais pas si vous vous disputez ou pas.

You never tell me anything, so I don’t know if you argue or not.