After everything he saw at Luna's rig, Jasper has voluntarily decided to take the chip. This tragic reveal is executed in a beautiful way.

Did Abby really take the key?

After arriving in Arkadia, A.L.I.E. ... While Pike and Kane battle it out, Raven enlists Abby and Jasper to help her destroy the key inside her, but their efforts are trawled by A.L.I.E. followers, with help of Jackson, Abby is captured and coerced to take the key by A.L.I.E. torturing Raven.

Does Jasper ever forgive Clarke?

Jasper hated Clarke and wasn't ready to forgive her. By the end of Season Three, it was implied that Jasper finally forgave her when he was apologetic to Monty for blaming him and Clarke and that he was done blaming. However, he was chipped at the time.