[s12e23] At Last Here

: After weeks of bickering over patients and Meredith acting as a barrier between Riggs and Maggie, the two have a heated argument in the hospital parking lot. The tension turns into a passionate encounter, marking Meredith's first significant romantic step forward since Derek’s death.

: Alex is tired of waiting for Jo to marry him. He gives her an ultimatum: marry him or they are done. Jo refuses to give him a straight answer, leading to a devastating breakup. It is hinted that Jo has a deep secret preventing her from saying "yes." [S12E23] At Last

It establishes as the primary event.

Explain the and why his arrival was so controversial. : After weeks of bickering over patients and

Her refusal to marry Alex sets the stage for the reveal of her "Paul Stadler" backstory. He gives her an ultimatum: marry him or they are done

Reaches his breaking point with Jo, choosing to walk away rather than stay in limbo.