 If you liked
Seishun Pop!
|
 ...then you might like
Hetakoi
|
The fact that boy engages in a sexual relationship with another girl trying to forget the one he truly loves is quite similar in both series. Also, the relationship development (except for the ending, which I won't spoil) are also similar.
If you read Seishun Pop and you're searching for something less psychological but more drama-intense, try Hetakoi. If you read Hetakoi and you're searching for a short drama with a little bit of psychological themes and a lot more ecchi/sex scenes, then read Seishun Pop!.