Worry

At first she was worried when Tsunade returned to Konoha.

How can she compete with a goddess?

Working with Koharu-sama she knew that Jiraiya was offered the Hokage position. Why, oh why hadn't he taken it?

She thought back over their years together and recognized the truth of the matter.

Although Tsunade may occasionally have his eyes (well, maybe more than occasionally) Yoshino knew she'd always have his heart.

After that it was easy to stop worrying.

Well, a little bit easier.