I still don't understand 1 thing about the ending. So in the timeline that we're playing Booker, is our Booker the real one or Comstock is the real one in the timeline?

As far as i understand, both Booker and Comstock cannot exist in the same timeline except 1 of them goes to the other

Cause if he baptized then he will be Comstock and if he don't, then there won't be any Comstock

When we were saving the smith, we entered the timeline to become the martry of revolution. What happened to our original timeline where we came from? Booker no more?

These are the reasons why i felt the ending wasn't satisfying for me as it explains nothing

From my understanding, basically its like this: the only way to prevent Comstock from stealing Anna/ Elizabeth is to prevent Comstock from being born/ created at the first place. Remember what Booker said by "smother him at his crib"? - it means it's better to cut off the source of all the problems - which is the birth of Comstock. This happens when Booker decides to be baptised and then be "born again" in the new identity of Comstock. That's why the baptism scene was emphasized so many times - it is the point where Booker decides to remain as himself, or choose to become Comstock, hence the necessity of killing Booker before he makes any decision.

Do note that the birth of Anna/ Elizabeth only happens after if Booker the decision of not taking the baptism and choosing to remain as himself..

Nothing to debate. If Elizabeth is Booker's daughter, and during Baptism how on hell can a full grown Elizabeth is around to drown him?