Yes. In episode 173 Mamoru leaves for America. Usagi goes to the airport to say goodbye, wanting to send him off with a smile on her face. She can't and breaks down into tears. Here's the best part, Mamoru gives her a present....which happens to be a ring. it's like a heart surrounded by small stones. (diamonds? I think so) and THEN he gets on his knees, puts it on the ring finger of her left hand, (!!!!) stands up and ... Ai Shiteru, Usako. Ai Shiteru is Japanese for the greatest expression "I LOVE YOU".
He ALSO says he loves Usagi when in Sailor Moon Super he is being chased by Fish Eye who is trying to seduce Mamoru. Fish Eye asks Mamoru why he won't give into Fish Eye. And Mamoru looks at Fish Eye and tells him, "Because I love Usako!"
But ya know what? What if he hadn't ever said I love you to Usako....would it really matter? Just how important are those 3 little words? *SAYING* I love you isn't really the most important thing. Usagi knows he loves her, we ALL know he loves her, it's obvious in the way he holds her, kisses her, saves her butt, and cries over her. It's obvious in his loyalty and devotion to her, to them, and their life together.
As nice as it is to hear and say 'I love you' those 3 lil words are just words. Often times, actions speak louder than words. All the times Mamochan was THERE for Usagi....never looking at another girl, always putting Usagi before himself and his own needs and life - THAT is love.
I once saw an interview during Nagano's Olympic Games about Japanese people. There, I learned that in Japan, saying "I love you" is just not as in America or elsewhere in the world. The man also said that a Japanese couple could live together for more than 25 years and not even say "Aishite" once!!! This specialist also said that the great "hit" right now in Japanese shows was to actually say the words! This may be weird for Occidental people like us, but it's part of Japanese culture not to say the words! Therefore, the fact that Mamo-chan only said "aishite" twice, doesn't mean that he doesn't love her. On the contrary, these two wording of his love for her is quite impressive for a Japanese man! Japanese are expressives, not talketive like Occidentals! So, it's only natural for Usagi not to be submerged by "I love you"s!