It's a 2-chapter manga from Makono Yumeno. Riku is part of an all-boys idol group and fell in love with one its' members. The rest of the group were unnamed.
It's from Miki Aihara of "Hot Gimmick". I'm currently reading this and I think the third guy will be the third wheel basing from the cover and from Aihara's writing style.
"Full Moon Wo Sagashite"
It's from Arina Tanemura of "The Gentlemen's Alliance". I watched the anime before and dropped it at episode 11 (out of 52 episodes!). But I'm having second thoughts as I tumbled upon this picture. For those who have seen or read this, is this a reverse harem?