Kanye West is back huffing laughing gas again, multiple concerned sources tell The Post. “When he [West] got back to LA he got dental work again and I think that’s when he relapsed,” a friend said, referencing his return to the city after six months away at the end of January. The 47-year-old rapper and clothing designer’s recently erratic behavior has worsened by using nitrous oxide – commonly known as laughing gas, an anesthetic. A second source told The Post West’s nitrous use has been a major pain point in his relationship with wife Bianca Censori. “The nitrous took over...