You can find the full 28-track album on all major global music platforms. Most of these services offer an option to download for offline listening with a premium subscription:
Because This Is My First Life (Original Tv Soundtrack) - Spotify
The original soundtrack (OST) is as essential to the drama's identity as its philosophical dialogue and realistic portrayal of modern relationships. Featuring a blend of indie-pop, soulful ballads, and upbeat acoustic tracks, the OST mirrors the slow-burn evolution of Nam Se-hee (Lee Min-ki) and Yoon Ji-ho (Jung So-min) as they navigate a marriage of convenience. Where to Legally Download & Stream