Chitoge admitting to Raku that she's not been good at making and keeping friends for a long time due to her family's sheltering of her and Claude, as her bodyguard, micro-managing all aspects of her life and scaring away all potential friends.
The arc where Chitoge mistakenly believes that Raku has told her that he dislikes her and could never see the two of them together as anything not forced by their families. She ceases contact with Raku for the rest of the Summer and then refuses to socialize with him once they're back in school, speaking to him coldly because she thinks that he thinks that the two of them never meant anything to each other. What makes this worse is Raku's reaction to how Chitoge's acting towards him - he's hurt and devastated that the girl he'd gotten so used to spending a lot of time with and had at this point come to think of as a close companion now wants nothing more to do with him.
When Paula reveals that she was hurt by Tsugumi leaving America because she's always looked up to Tsugumi and just wanted to hear complimentary words from her, and cries into Tsugumi's arms after Tsugumi does just that.
Many moments in the Hana Kirisaki arc. Especially when Chitoge fails to convince her mother to spend Christmas Eve with her in a phone call, and in response discards her signature red ribbon that was a gift from her mother, symbolically disowning her mother and giving up on any chance of ever bonding with her and when Chitoge and Hana reunite and reconcile at the airport, with Chitoge letting her mother know she loves her, even moving Hana to tears as they embrace.
In Shuu's crush arc, we realize that Shuu has a crush on Kyoko, the teacher, who is getting married in a month. Shuu decides not to do anything and just accept his heartbreak, spending the whole arc with a fake smile on his face. However, Raku points out that he's lying, he has regrets, and he should do what he wants to do instead of what's right, so he decides to run to her taxi and tell her his feelings for her. She tells him that she's glad he's not letting his youth go to waste, and that she wants him to be happy.
When Chitoge loses her ribbon and spends days feeling depressed about it. Especially when it appears as though the ribbon gets shredded by an incoming train and she breaks down in tears about it...before Raku reveals that it was the replacement ribbon he'd bought for her that got shredded, and that he retrieved her original ribbon in-tact, turning Chitoge's tears into tears of joy and relief.
Ruri telling her grandfather the truth and slowly breaking in seconds. Her trying to explain that she's happy with the friendships she's gained over the series doesn't make her Broken Tears any less painful to observe.
Chitoge breaking in tears over being unable to say goodbye to her friends and Raku after Claude locks her up until their flight to America will tug at a few heartstrings if one isn't filled with a desire to hurt Claude.
With Nisekoi nearing its end, regardless of whichever side of the Ship-to-Ship Combat you are on, it's sad to see the girls you have come to love being rejected by Raku or voluntarily giving up their love.
In chapter 213, Raku's reaction after Chitoge disappeared without a trace. He can't even try to cry.
In chapter 215, Chitoge running away from Kosaki.
In chapter 225, Kosaki finally confesses her feelings to Raku while knowing full well what his answer will be.
It's not even the fact that Kosaki confesses; it's the fact that Raku bursts into tears after realizing that his childhood crush liked him back the whole time, but it's far too late to do anything about it.
And then the subsequent chapter just rubs salt into the wound. She tells him to go and pursue Chitoge, giving him her key before he does. As soon as he leaves, Ruri comes to check up on her, and the poor girl's on the verge of tears. Raku meanwhile figures out that the locket fits Kosaki's key, and discovers two notes written to the future versions of themselves. Raku's isn't so bad, even a little funny, but Kosaki's had her speculating on her future life and then asking Raku directly if he still loves her after all this time. It's almost enough to make him start crying all over again.
In chapter 227, Be honest, how many of you cried with Chitoge after they both confessed?
