Your questions are pretty basic. No ofense, but I would suggest you take a basic online course in probabilty theory to get a bit deeper into the subject
In short:
I am wondering, if I keep winning will my chance of winning further decrease ?
In normal betting games, different rounds are typically independent from each other (so that the outcome of the previous round does not influence the next round). That means for any round: It does not matter what your result of the previous round was. Whether you lost the last 5 rounds or you won all of them has nothing to do with the result of the next round whatsoever.
Let's say, I am playing with 70% chance, and increasing my bet amount after a loss, and keeping enough money to cover till loss streak of 20. (which is insane!), and I continue to win, does it mean at some point my loosing streak will exceed 20, and bust all my bankroll ?
This is a popular strategy, however, will fail in the long run under normal circumstances (i.e. when the house has a small edge).
The probability seems small to lose 20 runs in a row, however your average gains will also be relatively small as you have to maintain your safety net of the money of 20 rounds.
This strategy is very similar to putting your money on 35 (out of 36 + 0) numbers on a roulette table. Your probability to lose is small, but your gains are also small.