Influence of OthersThe rest of the party obviously have their opinions on the relationship between Luke and Tear. They generally tease Luke about it because he is extremely oblivious to the whole situation. Teasing aside, the party does encourage Luke to comfort Tear and vice versa, which is a large factor in how their relationship develops.
JADE is the first to actually comment on their relationship. He tends to call their arguments "lovers quarrels" any time they break out in front of him. Tear constantly reminds him they do not have that sort of relationship, but he can see the truth. Jade is an adult after all! He can tell the two teenagers have crushes on each other. Other than that, he picks on Luke for being very dense and not realizing Tear's feelings for him. Jade tells Luke to go to Tear's side when she finds out she will die from repeated exposure to the miasma--He knows Tear wants Luke to be around when she is upset. He also questions Anise if she is planning on murdering Tear as opposition because he knows that she wants to marry Luke. One would assume, then, he actually considers Tear "competition" for Anise. Jade likely thinks that Luke has feelings for Tear as well, but is just too stubborn to admit it. He gets amusement out of watching them together and making fun of Luke. Even so, he pushes their relationship forward a little by advising him in the right direction.
GUY is Luke's best friend and also can easily see the feelings that have developed between Luke and Tear. He tends to take part in teasing them, only because he knows it is true. I believe even though he did not want Luke to sacrifice himself, he still grabbed onto Tear to make sure she would not get hurt while he was doing so because he knew Luke would feel horrible if anything happened to her. He, like Jade, also calls their arguments "lovers quarrels" occasionally. He generally does not tease Tear to her face. The one and only time he did by saying that she had Luke whipped into shape, she hugged him as punishment for saying "stupid things." Though some people support the relationship between them, I think Guy couldn't betray the feelings of his best friend and he knows she loves Luke anyway.
ANISE automatically assumes that Luke and Tear are together, since she comments on how she "might be in the way" if she walks around the Tartarus with them. Sometime later she complains about how Luke is always with Tear, and occasionally makes other remarks about the two being together. I believe that Anise helps Tear realize her feelings for Luke because she keeps pointing out how they are always together or how Tear is in the way of being able to marry Luke. Even though Tear disregarded it out loud, she probably thought about it more and more as Anise kept saying it. Tear may have been in conflict with her feelings for him and I think Anise probably helped if she was. She also teases the pair occasionally, telling them it was suspicious for the two of them being alone in the dark in Tataroo Valley. Deep down, Anise knows she has no chance with Luke (and is likely not really interested in him that way anyway). I think she ultimately ends up rooting for their relationship to work out, even if she does not vocalize it.
As Tear's only "real competition" for Luke, NATALIA leaves somewhat of an impact on Tear's feelings. When she first found out that Luke was technically engaged to Natalia, Tear did not say anything at all. When they finally meet and Natalia accuses Luke of cheating on her with Tear (whom she calls a maid), Luke tells her he would never "touch a chick as cold as that." Tear, again says nothing and simply looks at Natalia. She voices how she feels inferior to Natalia's beauty before Guy tells her she is beautiful too. If she had any feelings for Luke at all at that point, she probably felt guilty for having them for a guy who was engaged, especially to a woman who she thought was a lot better looking than she was. As the journey progresses, even Natalia notices the chemistry that Luke and Tear have together. I believe the only reason she has an easier time doing that is because she finds out that Luke was not the one who made the promise to her. Natalia knows that Luke doesn't feel that way about her and more than likely assumes that Luke has feelings for Tear. Though Natalia never really takes part in any teasing of the pair, she indirectly tells Luke to go for it by saying she will support him as his childhood friend, rather than forcing the engagement on him.