Akise Aru really really likes Yukiteru. He's shown to be immensely interested in him, and follows him around, sticking his nose into Yukiteru's business. And his actions towards the end can be interpreted as trying to drive a wedge between Yuno and Yukiteru by digging up dirt on Yuno's supposed past. Love for Yukiteru seems the most likely motivation for much of what he does.
In chapter 17, Akise admits in secret to Yuno that he likes Yukiteru beyond friendship, leading her to panic momentarily when he purposely wraps his arm around Yukiteru's waist (or even appears to touch his ass) to aggravate her.
In chapter 48 Akise declares to Deus that his love for Yukiteru is genuine. Deus tells him it was part of his programming Deus put in him to make him the Observer. Which really makes you wonder about Deus himself.
It comes to a head in chapter 50 when Akise tells Yukiteru that he wants to protect him no matter what, declares to Yuno "I won't hand Yukiteru over to you!", and forcefully kisses Yukiteru. All this in front of Yuno, who goes crazy even by her own standards. In the anime he also calls Yukiteru "my beloved Yukiteru."
Yuki did not react negatively, just surprised.
There's also Mao, who's not-so-secretly in love with Hinata - she can't stop looking at/thinking about/lusting after/recording in a diary Hinata's impressive bust (for a 14-year-old). Comes out clearest when Mao takes a picture of Hinata in her underwear.
At one point Hinata says "Forgive me. I hope I didn't take advantage of your feelings," when she gets Mao into a bad situation. Mao also teases Hinata a little when she becomes chummy with Yukiteru.
In the Redial OVA Mao becomes unbelievably happy when she accidentally touches Hinata's breasts. She's still happy even when Hinata is calling her out. And then Yuno, of allpeople, touches her breasts too.
Later on Hinata reads out loud the entry about the above incident causing Mao's nose to bleed.