On reputable sites, especially on the ones presented on this forum, there's no such thing as "casinos tweak the games to make sure you lose eventually". When you have a long losing streak - it's just pure probability catching up with you, or as we here call it "bad luck".
We can assume that way since the casino is reputable, but we also can’t be too confident saying they can’t tweak the games. It’s usually not the casino itself but the game providers who could do that if they wanted to. There’s always that possibility, especially since casinos generate huge revenue and providers might have a share in it depending on their agreement (which I believe they do).
So in the end, if we want to enjoy gambling, we just have to trust them. And if we keep losing, maybe it’s best to stop and just look for another casino. That’s not even hard to do since there are plenty of reputable casinos online, just start by checking the ones recommended here in the forum.