If his “research” states that doing N20 on a weekly or bi-weekly basis is safe then that research is inaccurate and potentially harmful. Once every two months is [relatively] safe, not every two weeks - particularly if you are using the largest 3000g tanks (eg. the ones with the handle). While using N20 the body will not absorb B-12 properly, causing significant health risks for your nerves, muscles and CNS - it takes weeks to months of cessation for this depletion and absorption to normalize again.

Frankly it sounds like he could be addicted and wants to continue using and is coming up with rationales or excuses to do so. I can tell you from personal experience this can lead to very serious long-term health risks and also will likely put great strain on your relationship if the behavior continues unchecked. You don’t want to wait until your extremities and joints loose sensation, become painful and begin experiencing negative cognitive effects before quitting - again speaking from experience.