When did English drop thorn?

I have a few questions about the letter Thorn ("Þ", "þ"), that once upon a
time was used in English to write the sounds now written "th".

- When was the letter dropped from the English alphabet?

- Why did it happen?

- Was is used for the sound in "thin", or for the sound in "this"? Or for
both? (BTW, were the two sounds distinguished at that time?)

- How and when did the "th" digraph assume the sound it has now in English?
It doesn't have this sound in any European language (apart Albanian, but I
guess that its orthography is quite modern).

Thanks.

_ Marco