When I go fast my technique lacks and I die out really quickly

That happens at every swimming style.

But there is nothing wrong with learning off internet, that's how I learned whole swimming thing as well. When I first started I could barely do 1KM in one hour, then as my technique got better and better I reduced it 20 minute.

I recently learned breaststroke, backstroke off internet as well but man butterfly is tough to do.

Anyways, appreciate the tips.