Hello, again) I'm so sorry...

I have been  away, (you are emphasizing that you are back now, so you use present perfect to connect past absence to the present), for such a  long time, (“time” is a noun, which means that “such a” is used to add the emphasis). I'm sorry I didn't answer some people, (the phrasal verb “answer to” has a different meaning so only answer is needed here), who wrote me. Don't be angry with me, please! Forgive me) I'm here again and will try to be here every day) I missed you/have missed, (do you still miss us a little because you are waiting for more communication, or have you finished missing us; use present perfect for the first, but the difference is small, so you have a choice here), so much...

this is a very nice apology. I’m sure everyone is glad to have you back.

Hello, again). I'm so sorry...