I never like Usagi and Mamoru's relationship in the anime(just the anime. They're my OTP in the manga) so I already pair Mamoru with other people anyway. I always felt there was more chemistry between him and Setsuna in the few interactions they had than the entire series with Usagi. Setsuna seems like the type of woman Mamoru really wants and I always got the impression he only tolerated Usagi because of their destined future. I even remember a fan theory back in the day of Sestuna being Chibusa's mother because of their red eyes and the fact that Setsuna seemed to be more of a mother to Chibiusa than Neo Queen Serenity.
I know some people will say that Usagi and Mamoru are "opposites attract" and I'm a fan of it myself, but there are times where people can be too different from each other. I never saw Usagi bring out a different side in Mamoru and vice versa. In fact, Mamoru seems down right bored with Usagi while Usagi is horribly insecure about their relationship(I know that there's some natural insecurities in relationships, but Usagi is so afraid Mamoru will leave her for someone "better" that she becomes insanely jealous and clingy when he just looks at another woman outside of the other senshi. That's usually the sign of a bad relationship).
I'm also not a denying that Mamoru doesn't care for Usagi(he's shown that too many times to count). I just don't think that he's in love with her and feels obligated to her. I'm also not a Mamoru hater. He's not my favorite since he since he never became more than a token boyfriend(I prefer him way more in the manga where he actually has a personality), but I do like him.
Mamoru does love Usagi in the anime he has shown that he loves her and this is a canon fact. Also he never had as much chemistry with Setsuna in the anime as he did with Usagi. He shows so much. Also Setsuna is not the type of woman Mamoru really wants, Mamoru needs someone more fun and adventurous to keep him interested. Also he does not put up with her because of their destined relationship. This is bogus as they were growing closer even in the animated continuity to each other without their memories. For instance, in the anime, when Mamoru/Darien throws the rose at Beryl's heart and she begins to die, she says to Mamoru, "Your love for Sailor Moon is killing me." He then lays on Usagi's lap dying and looks at her face and tells her "Sorry I made you wait Tsukino Usagi with the odango atama." He doesn't call her Serenity here. It is Usagi he is speaking to. The biggest proof comes when Mamoru doesn't even remember ANYTHING about loving Usagi and yet comes to care for her SOO much in the Doom Tree series. Together they go from taking care of a baby, to Mamoru holding onto Usagi's hand as they play at the lazer arcade, to Mamoru reaching out to save Usagi from the Doom Tree, wanting so badly to protect her. That is him caring for USAGI. Not Serenity.
Also I saw many times in the anime at how Usagi brought out Mamoru's fun and carefree side and Mamoru brought out Usagi's dedicated and responsible side. Such episodes like the babysitting episode come to mind. Also he never seems bored with Usagi but in fact is always entertained by her.
Also, in Sailor Moon R , at the beginning when they are finally together, the couple is out on the lake and when they go up on the dock, Usagi trips and Mamoru laughs and hugs her saying, "You're such a klutz....but your *MY* klutz" and they kiss deeply. They are not too different and have many things in common and get along very well.
As for Usagi's jealousy she would be jealous and clingy no matter who she is in a relationship with. She even shows jealousy about her family and friends giving her attention. Usagi desperatly needs attention it is just who she is.
Also again you would be wrong, the canon as well as the whole anime shows that Mamoru loves Usagi and is not obligated to her. That is simply an infactual lie. He does not stay with her because he feels obligated to her, he genuinely loves her. If he didn't then he wouldn't fight so hard to protect her and would just be her friend. His spirit in R would not have formed the Moonlight Knight just to protect Usagi. Also even in the beginning of the anime when they were having those playful fights they were teasing each other because they secretly liked one another and anime material shows they did have feelings for each other even then. So yes Mamoru loves Usagi, anything else is uncanon.