My feelings on this series are complicated, because I like how it's done basically all the way till the last 5 minutes, so I've been grappling with myself on whether I let those 5 minutes determine how I feel for it or if I take it and try to negotiate what I take away from it.
Because I could go on about how I think it's important Lara's bodily autonomy became a focus in the plot over the fairy tale idea of true love, kind of like a plot twist scenario that wasn't really a plot twist if you thought about how her father has been treating her up to this point, and the fate of her mother and Grace as well was because they both had to be forced into finding true love while young. In that perspective, the ending to me is Lara breaking away from all those expectations to build a life for herself completely separate from those things. I think people who say she could build independence while staying in Shiga are missing the point a bit. Her sister is there, her slumbering family members are there. Even if Mari and her friends help her establish a life there, there are markers everywhere of the mermaid she used to be and the true love she was trying to achieve that was hurting both herself and her relationship to the people that meant the most to her. I think the fact that Mari and herself talked about wanting to live together in the future shows Lara isn't abandoning her love for Mari or her found family and friends. Realistic or not, this is after all the story of mermaid turned human, Lara had to leave to get a fresh start. I myself think 6 months is too soon, but after thinking about it more, the exact time frame is more a nitpick than anything.
However, I am also sick to bastard death of yuri and the relationship between young girls being treated as this pure and untouchable thing that transcends "love". It's my problem with Cosmic Princess Kaguya as well. Physical intimacy let alone sexual intimacy is seen as something that introduces conflict to a pure relationship. It's the kind of thing where these girls mean more to each other than friends, but they can never call themselves girlfriends or explicit romantic partners. As much as I enjoy them, I won't defend SayoLara, CPK, or really even any original anime yuri-adjacent work from this.
So we've dismantled the fairy tale and the need for young women to find true love, instead valuing independence and living for the sake of living -- which is fair, I don't hate this -- but Lara still loves Mari, and Mari still loves Lara, and they're definitely still going to live with each other as adults.... sooo, what's the word for that? Are we ever going to be allowed to say it? Let alone, will they be allowed to say "I love you" to each other? I'm okay with beating around the bush for the sake of building intrigue, but doing it so much only for them to never acknowledge it to each other is just cowardly.