New problem, head crack?

[alundra]

I hope that our head can resist more because when i saw threads with T2, T25, T3... my boost is still stock.

Where is the weakness come from?
How to solve it?
When i search why it's cracked, it seems water pressure but my thermostat was new for one year now, before it no crack from here.
I don't know how to remove the head, my level in mechanic is just to change brake disc and brake pads

Tomorrow I will a company specialised in aluminium welding, perhaps they cn help me.

Cheers.