Some of the people who have been ranting against Yui have not been paying attention.
His acquaintance with Chitose dates to when they were children; Yui was the boy who got her to start crafting
objets d'art, and her reaction to that earlier interaction meant a great deal to him.
And he never sought to
take things from Kinosuke; things were
given to Yui that Kinosuke wanted. There has been no indication that Yui knew the motivation of the girl who dated Kinosuke in an attempt to get to Yui, and Yui didn't subsequently date the girl. Nor does it so much seem that Kinosuke resents Yui for things going to him; Kinosuke resents that Yui didn't
value the things that went to him that Kinosuke wanted. (But no one should have valued that earlier, scheming girl!)
Yui's great error was in not
looking for Chitose when they were older.
Had this story begun with Yui as the central character, discovering that the one person about whom he had really cared was now in an initial courtship with his brother, almost every reader would be rooting for Yui. He's not a villain. He's a decent person whose timing is tragic.
Also, if someone needs an emoticon not on a button above and not on his or her keyboard, then the thing to do is to copy it from a Unicode table. Here is the anger emoticon: “

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