Chiba Mamoru / Tuxedo Kamen / Endymion
Mamoru
Chiba, her eternal love, we could call him like that. They were together in
the past, they are together in the present and will be in the future…
In the manga their relationship begins with arguing and him making fun of her
calling her Odango Atama (in English he calls her Meatball head). At the beginning
she hates that nickname but the later she becomes quite fond of it. 
They are driven together by unknown forces during the Dark Kingdom arc, and they don’t know why till he doesn’t save her from a deathly blow that makes her remember her past life and the fact that Mamoru is her Endymion.
In the manga their relationship is less rocky as in the anime (hell in the second series of the anime I came to hate him), but still there are moments that make their love even stronger.
He was the prince of Earth in the past, while she was the princess of the Moon, they shouldn’t have met and even less they should have loved each other, but nobody can stop love, and so they kept meeting in secret till the moment the Moon was attacked and he died protecting his love – she committed suicide because she knew that without him she wouldn’t be able to live. In the present it seems that this tragic way is taking again the place, a little differently, he is possessed by evil, she uses the sword to kill him, and then commits suicide. Luckily, they survive. And together with uniting their powers they save the day, staying together on the Earth, vowing to protect it together.
In the second arc, the Black Moon arc, they don’t broke up as in anime (thank you Naoko-sensei) even thou there is a moment when Usagi is quite upset with him, it almost seems she is jealous of Chibiusa, who she knows is their daughter, but no, she actually hates the fact that when Mamoru said to his future self that he’ll protect her, he didn’t considerate that maybe she would protect her with him, he used “I” and not “we”, which lead to all the chaos, like Chibiusa (who has a giant Electra complex) becoming Wicked Lady and again dominating him in to hating Usagi. But then again, their love is stronger, and when, after Pluto sacrifices herself, Sailor Moon disappears, he is driven to her and they are together and their love again triumphs, but this time there is also Chibiusa to help their power to be stronger.
The third Arc, the Infinity arc, when it comes to their love is quite uneventful, if not for the jealousy between them (Well Haruka did kiss Usagi on the lips, so probably that means cheating). It’s actually funny at the moments how both are jealous, but then fortunately for a moment Chibiusa gets over her father complex, and gives them the opportunity to make up. In this arc there is a really sad moment, because this time there is no Mamoru possessed, but they come to think that Usagi is dead, so there is a scene of him who is totally devastated by the thought (I can’t believe nobody noticed that being Chibiusa still there, meant she wasn’t dead).
And
then comes the forth arc, the Dream Arc. Their life is nice, they love each
other, they have a working relationship and then there is the curse, the black
rose that makes him cough black blood. Because he doesn’t want her to
worry too much, he rejects her and says to stop hovering over him, hurting her
(aside that Chibiusa’s huge father complex is back). But then again, always
she manages to explain him that she loves him and that she will be with him
always and it doesn’t matter if he is ill and then he accepts her back,
and she gets cursed too. So they again fight together uniting their power defeating
the evil and becoming King and Queen.
The
Stars arc, which is the last, features Mamoru departing to go study aboard,
giving Usagi the ring, and then Galaxia takes his star seed making him disappear.
For the girl that is such a shock that she completely forgets that it had happen
and says he departed as planned. She finds him again as evil under the power
of Galaxia, where he again attacks her and makes her suffer… and then
he is killed (yes because Chibiusa vanishes, that means there is no future),
in front of her eyes. Usagi takes her decision, there is nothing to lose for
her anymore, she defeats her enemies, and saves the day… this time she
does it alone out from desperation. She manages to save everyone and put the
time on her track and her dream is fulfilled.
“Mamoru, can you say it again?”
“I said it 50 times last night.”
“Just once more.”
“Last time… let’s get married Usagi!”
- Stars Arc, Act 52