| With steady observational advances, the formation of massive stars is being understood in more detail. Numerical models increasingly suggest that accretion discs play a key role, and binarity seems to be an inevitable outcome. Indeed, the vast majority of massive stars are found in binaries (up to 100%). However, our understanding of the innermost regions of discs around massive stars and their associated binarity remains limited due to the rarity of such objects and observational challenges, particularly the lack of adequate diagnostic lines in the near-IR. In this talk, I will present recent advances in understanding Massive Young Stellar Objects (MYSOs) through long-baseline near-infrared K-band interferometry (VLTI). A key focus will be the investigation of diagnostic lines, such as Brγ, CO, and the recently resolved Na I and He I, to gain insights into the accretion and ejection processes occurring at the innermost au-scales of the star-disc interface around MYSOs. I will also discuss current statistics on young high-mass binarity, tracing separations from 2 to 300 au, and compare them with pre-main and main-sequence stars, revealing an increasing fraction of binaries as these stars evolve. |
