ok here is the thing with streaming. Streaming ability is, to a huge degree, dependent on how good the muscles in your arm are trained ((next to aim of course, which is the other component). Think of it as weight-lifting, where faster streams mean heavier weights. If you freeze up during the streams, it probably means that you put up more than you can lift.
That being said, you need to train your arm better. People say "play more", but that is only a half-truth, as there are some training methods that are very effective and others that are not:
If you want to get good at streams, you have to play the right maps over and over to get good at them. You can't just play something like image material, since that would be akin to training with 300kg when you can only lift 45kg. What you'll want to do is train with 45kg until you can feel your arms-- in other words:
what you need to do is playing maps that are slower, so you can stream them comfortably, but still train you because the streams just keep going forever.
https://osu.ppy.sh/s/72474When you play this, you'll feel the muscles in your arm "heating up", really soon. That's the feeling you want to get. Play the map that feels most comfortable and try to keep going as long as possible. Rinse and repeat.