In your first post you mentioned 165 kg deadlift for 5 reps and now you lift 110 for 5 reps ? So you detrained that bad ? You are 18 ? When was this 165 kg deadlift ? In your previous life ?
Belt is important.
Do not squat high. Lower the weight to what you can squat to depth and continue from there.
Buy the book. If you already have it then read it. Twice.
I did 5 rep for 167.5 kg at my top on my latest program. It was about 4 months ago and some weeks after that I ate really bad/little so I quickly lost strength and weight. With SS I am at 110 kg right now. In order to squat deep and keep good form I think 90 kg is a good weight. It is like a 10% deload. However, I have trained for a pretty long time and my squat never seems to surpass 100 kgs...