He goes back to the Beta timeline in order to save Kurisu. He fails once and this is the start of Steins Gate 0. In S;G0 Okabe chooses to stay in this timeline and keep Mayuri save by sacrificing Kurisu so Kurisu is still dead in this timeline.

Does Okabe save Kurisu?

In episode 23/24 thanks to a message from his future self in the Beta line, Okabe realises that he can trick fate and save Kurisu but keep everything that made him who he is in the past 3 weeks (actually more like months because of his constant time leaping.)

Does Kurisu show up in Steins Gate 0?

Kurisu is one of the main characters of Steins;Gate, a major posthumous character in Steins;Gate 0 via Amadeus. She is briefly mentioned in Chaos;Child, and she communicates via the in-universe Twitter (Twipo) in Robotics;Notes and Robotics;Notes DaSH.