Deckard2 said:
I always wondered what Lando and vader's original agreement was that would have justified him betraying his friends?

1st change

Give Han to Jabba the Hutt

Leia and the wookie are not to leave the city.

2nd change

Lando is to bring the Princess and the wookie to vader's ship

Apparently it was simply "Let me chill here, keep your friends unharmed for a bit, and I'll capture some shmoe you've never met, and then I'll leave you be. We cool, we cool."

Did Vader torture Han so that Luke would feel Han's pain through the force and then Luke would come to Bespin?

That was always my impression.