1.Do not worry as no one commits suicide who gives such threat.One who does never gives priorwarning.
2.You are an adult and nobody can force you to later your own choice or decisison in life.
3.SO you can always start reading away from your parents provided you can sustain yourself in all respect.
4.For this you need not send or write any letter though there is no harm if you leave your home.go else where and inform the local police about you going somewhere else willingly.
5.However parents would always rebuke a child to reform him and these may not be tortures.So take your decision after much deliberations with your peers and without haste.