He went so far as to give young Martin a note to be opened in 2017, warning him of his death and explaining exactly what to do to prevent it from happening.
In the midseason finale, the Legends found themselves joining forces with a young version of Martin Stein.
Some dealt with young Martin on board better than others, and Jax understandably had a difficult time.
Jax was not able to save Martin, and he decided that he needed to take a break from adventuring through time.