Quite a large House Edge at roulette. Even using different manipulations with bankroll management, you will still lose it.
We draw a simple conclusion - there are no working strategies for roulette, only luck on a short distance and stop playing it.
Yes, that's how it goes for roulettes and other the same game that don't really have any calculation and way to win against the house. So it's been quite a long for you to realize this matter and it took you several months. That's still better than nothing you've understood and still not realizing that there are those games that you have to depend on your luck, no matter how hard you try of learning to win against them.
Just play and relax. You will just go crazy if you will find ways on how to win on this luck-based game. Besides, there's HE that you can't beat. Just accept the fact that this game is one of these luck-based games where you don't need to crack your head to make a strategy on how to win.