I can't seem to remember nor find on my lists this manga (It is a oneshot). It was about a girl who has become the leader of her fathers yakuza group and her group is losing their territory to another group. To save her group she must get married to another groups leader. However, she has a boyfriend and keeps putting off the marriage and in doing so puts her group in danger. Her group gets attack and get saved by her boyfriend, which she finds out that the guy she is supposed to be married to is him.

I am very irritated i cannot find this after searching through all my lists. If anyone can help that would be fantastic.

Sounds like the second story from Natsukashi Machi no Rozione.