How about this:

1. A, in the beginning liked B. Upon meeting A, B became fond of A too. One sunny day, B brought her good friend, C, on her date with A. A then fell for C, who suprisingly likes A too.

2. O likes P and vice versa. O then tell P that he used to date Q, P's old friend.

3. R and S are so-called-best friends, but little that R knew that S likes him. R then pursued his dream girl, T, who is a friend of S.

4. W dated X when her boyfriend, Y left her. One sweet day, Y came back into the picture and W left X. Z, W's best friend likes X. They became close and when they started dating, Y left W again, and then came the problem when Z is faced with her loyalty to her best friend and her passion for X.

Now, who dare say relationship is not complicated?

*Based on true story. Partly changed to protect the protagonists.