I haven't forgotten you.
I don't like you.
'Ich muss dich vergessen' means 'I must forget you.'
Ich werde dich nie vergessen. - I won't forget you.
The "am" can mean several different things depending on what follows (it can mean at, on, in, by, most, etc.). "Ich habe" means "I have."
Ich habe dich vermisst or Ich vermisse dich. (I`m missing you).
Ich habe nicht gewissen means [I didn't know (a fact)].Ich habe nicht wissen is a common mistake (with the same meaning) among people who speak German as a second, or third language.===========================================================The correct conjugation is:Ich habe nicht gewusst, dass.... I didn't know that....If you want to say I didn't know as a stand-alone statement then the correct form is:Das habe ich nicht gewusstorIch habe es nicht gewusst
"Ich brauche dich" is "I need you" in English.
"Ich verstehe nicht" means "I don`t understand".
Ich hasse dich nicht translates as I don't hate you.
Kannst du nicht verstehen, dass ich dich liebe. - Can't you see that I love you?
"Ohne dich kann ich nicht sein" means "I can not be without you". It means "Without you I cannot be" loosely.
"Ich habe Kopfschmerzen und das nicht gefaellt mir" means "I have a sore head and I don't like it" or more literally, "It doesn't please me"