Male/female leads together early on and 2nd guy is trying to steal her

I was watching Boku no ita Jikann and was wondering if there were any like the romance in that. The male and female lead start dating early on and his senpai goes behind his back to try and steal her away. He sort of succeeds in getting the girl, but not because he stole her. (He swooped in when she was vulnerable after their break up.)

Are there any like that where the second guy is an asshole trying to steal the girlfriend of the male lead? Maybe he does get with her, but not because she cheats or anything. The male and female leads break it off due to a misunderstanding or something. The male and female leads get back together in the end.

http://mydramalist.com/1329-rebound
http://mydramalist.com/1393-long-vacation
http://mydramalist.com/81-autumns-concerto
http://mydramalist.com/2905-kingyo-club


And sort of..
http://mydramalist.com/2277-ikemen-desu-ne
http://mydramalist.com/15460-5-ji-kara-9-ji-made

I hope you enjoy watching the ones you haven't watched yet! :)

Doesn't quite fit but ...

Lovers
Hapimari: Happy Marriage
Fated to Love You (you can watch both the Taiwanese & K-versions if you like)
Loving, Never Forgetting

all had situations where a 3rd wheel tried to come between the couple who are already an item, but temporarily separate due to complications in their relationship. The 3rd wheel takes advantage of the situation & tries their best to make their case to the female lead. These guys aren't necessarily evil assholes though, they just want the heroine for themselves. That's why these recs aren't a perfect fit for what you're looking for, but close enough I think.