HELP ME FIND THIS MANGA.. i know alot of details but forget what the manga is called or who the characters are..

i remember vague details like the girl falls in a love with a guy who only falls in love with girls who already have boyfriends. then this girl realizes this and ends up becoming his friend. theres one scene where the guys girlfriend tells the main girl to not return photography book to him and tries to stop their friendship. in which the guy breaks up with her because his friend (the main girl) is more important than the girlfriend.

Theres a side story about the main girls brother coming into the picture, but he has a diffferent another last name because their parents are divorced. The main guy thinks the girl and her brother is dating, so he gives her a chance. The main girls' brother likes the guys childhood friend who loves cute things (esp. pandas). The childhood friend ends up being the main girls friend, and has a relationship with the brother eventually, where the friend gets mad when she finds out they have different last names and thought they were lying about being siblings! The childhood friend's sister is the main guys first love (which the main girl finds out by seeing a drawing of the sister in his sketch book). The childhood friend is beautiful and is often a model for the main guy for his drawings?

another thing is that the guy loves photography or drawing and admires his brother who was a famous photographer (who dies?)... the guys first love is his brothers fiancee? (who is also childhood friends sister?)

Is it Datte Suki Nanda Mon ? I haven’t read it in a while but I think this is it.