When i go to do the Chasing Echos quest (Talking to serena) I ask her to take me into the castle and she says i must lose my interloper becuase she doesnt take everyone into her home. Problem is: I dont have a Follower.

I dont have any quests that require followers and no side quests except like Visit this place and blah blah.

I have killed Aela, Vilkas,... Farkas is gone. I have tried turning my partner into a blade and she said okay get him ready for the ceremony. But i try talking to Serena again and no luck still.

Any Tips, Thoughts, Help will be greatly needed. Im not wasting 20$ on a game i cant finish becuase of a stupid glitch

Have you interacted with any dogs?

wait. when you wait long enough, if anyone is following you, it will say "your follower tires of waiting and leaves your service."

but check all your quests, misc quests, and do whatever you haven't done while someone was following you. also, i think dogs and trolls count.

I have done the quest for Masque Vile. I had a dog once but i killed it too. I always end up killing my followers so.

I waited for about 7 in game days with no luck.

I posted this problem a day or two ago, literally the exact same thing. I murdered my follower in cold blood, and it didn't work. So, I had to find a save where I still had the "missing" followers with me and start over.
When I loaded it up and saw Illia, I met her with an arrow to the face for breaking my first dawnguard playthrough.

We NEED billboards that work the same as the follower terminals in new vegas smh.

Reload a previous save and see if it fixes itself.

takes longer than 7 days. check your house(s). make sure you don't have any inactive followers who you have told to go home.

i would reload a previous save but i hadnt play the game in 3 months before i played it yesterday and so it would be like harder to get back up then just to start on my level 10 account

did you ever use dead thralls? if so use the flame cloak spell to clear that up because dead thralls still count after being murdered or disappearing in your travels

You mean reviving people and stuff like that?

I can tell you from experience that this HAS to be a glitch. I had J'zargo at the time I did the quest and actually didn't dismiss him until after I was bitten by Harkon and became a Vampire Lord. Having a follower will NOT prevent this quest from continuing.

EDIT: I'm sorry. I misunderstood the point you were at. I had dismissed J'zargo by this point. The reason you have to dismiss your follower is because for this part of the quest Serana becomes your follower.