Sakura's conclusion-My way
After the 4th Great war, Sasuke had to accept punishment, preventing Sakura to confess her love for him. Naruto realized her sorrow and had comforted her. Someone else saw her sorrow: Rock Lee. Eventually, Sakura and Lee's relationship developed to a point in taking it to the next level.
Naruto already knew she had been interacting with Lee more often and seen her happier than before. Her happiness was his happiness. He was also busy checking in to Sasuke's whereabouts who was under custody. After Sakura and Lee's engagement announced, Sakura privately talked to Naruto to say "Thank you" for all he had done for her and that their friendship will be cherished always.
Naruto wasn't heartbroken when attending the wedding because he wanted both Sakura and Lee to be happy together. In fact, he supported them. Back when Sakura was dating Lee, Naruto was still a regular at Ichiraku and developed a relationship of his own with Ayame due to seeing her more often. Ayame was going to be the next owner of Ichiraku.
Lee was a very kind and supportive husband to Sakura, especially when she got pregnant with all of her mood swings. Sakura did get adjusted to living with Lee's overly youthful life 24/7 sooner than she thought. She became Naruto's first advisor after he became Hokage. She then leads the Konohagakure's Medical-nin Team. Happily married to the Green Beast Taijutsu master and has a lovely daughter.