The use of "sepas", the subjunctive form of "saber", implies uncertainty or doubt. In this case, the sentence would mean "I will love you forever although you might not know it".
Que Sepas means you know.
basically it means ill love you forever or i love you to death
"Although"
You meant: ...QUE SEPAS QUE... Quiero que sepas que te estimo --- I want you to know I appreciate you (informal you singular)
Siempre means always.
"Commo siempre" (I believe you mean "como siempre") means "as always" or "like always" depending on context.
"Although you left"
roughly: I am who you love, who waits for you and although I am not in your life, you'll always be in my life.
"Siempre y por siempre" would mean "Always and forever." Most often you will see "para siempre."
Yo soy boricua pa que tulo sepas translates to mean 'I am Puerto Rican, Pa you know it.'
'Siempre borrachado' means, 'always drunk."
"Siempre para tu" needs an ending. For example, "siempre para tu libro" is "always for your book". Siempre para ti is "always for you". Which one do you mean? take your pick.