Why does it say "Yiten" (future)?
Radak: It means that he gave to her. We find like this - "Az Yivneh Yehoshua" (Yehoshua 8:30), "Az Yavdil Moshe" (Devarim 4:41).
What is the meaning of "Manah Achas Apayim"?
Rashi citing Targum Yonasan: It is a choice portion (that is proper to receive it with Sever Panim Yafos, i.e. a happy face).
Radak: It was an honorable portion to remove her anger. "Erech Apayim" (Shemos 34:6) is patience regarding anger.
Radak citing Midrash Shmuel 1:8: Kiflayim (twice as much as Peninah and her children).
Radak citing his father: With anger he gave to her only one portion. 1 He was angry that Hashem closed her womb. Malbim - i.e. he showed that he was sad that he cannot give to her more.
Malbim: If so, Why does it say Apayim (plural)? This hints that he was pained doubly, for he loved her.