It could be due to a misunderstanding. Sasuke might have thought Sakura was involved in something harmful to him or his goals. For example, if there were false rumors about Sakura betraying him, his hot - tempered nature in the Naruto series could lead him to this extreme reaction without fully understanding the truth.
Perhaps in this fanfiction, Sasuke is on a path of self - destruction. He might be trying to push away everyone who cares about him, including Sakura. By putting a knife against her, he's not only showing his aggression but also his inner turmoil and the fact that he believes he's too far gone to be redeemed, so he's trying to sever his ties with her in the most brutal way.
She could try to talk Sasuke down. Sakura is a strong - willed character. She might start by asking Sasuke what's wrong, trying to reason with him, and reminding him of their past relationship, in an attempt to defuse the situation.
Perhaps Sasuke starts to notice Ino's unique skills and how they complement his own. Ino has her mind - related jutsus which could be useful in certain missions or battles. This practical aspect, combined with a growing personal bond, might lead him to leave Sakura for Ino.
One possible reason could be his sense of duty. Sasuke has always been driven by his goals for the village or his personal vendettas. Maybe he feels that his mission is more important than staying with Sakura and their unborn child, believing that his actions are for a greater good that will ultimately protect them as well.
In fanfiction, Sasuke might snap at Sakura due to miscommunication. Sakura could be expressing her concern for him in a way that he misinterprets. For instance, if she tells him not to go on a dangerous mission and he thinks she is trying to control him instead of just caring about his safety. Another factor could be the influence of external forces. Maybe there are other characters or events that put him in a bad mood, and Sakura just happens to be there at the wrong time, so he snaps at her.
One possible reason could be that Sakura has finally grown tired of Sasuke's aloof and cold behavior towards her. She might have realized that she has been constantly chasing after him while getting little in return, so she decides to ignore him as a form of self - preservation.
One possible reason could be Sasuke's continued obsession with his revenge - even after they got married, his focus on past grudges might have driven a wedge between them. Another could be differences in their life goals. Sakura might have wanted a more settled family life, while Sasuke was still drawn to his wandering ways in the name of protecting the village from afar.
Perhaps Sasuke was testing Sakura's loyalty or strength. He may have thought that if she couldn't withstand his aggression, she wasn't worthy of being in his life. Also, his own inner demons, like the hatred he carried from his past, could have flared up and led him to almost kill her without fully realizing what he was doing.
One possible reason could be Sasuke's continuous absence due to his solo missions. He's always away, leaving Sakura feeling lonely and neglected in their relationship. This lack of emotional and physical presence can gradually erode the bond between them.
Protectiveness. Sasuke has seen a lot of danger in his life. He knows Sakura is a valuable person, both as a friend and as someone he cares about. So his possessiveness could stem from his desire to keep her out of harm's way. He doesn't want any bad guys to get near her.
One possible reason could be that Sasuke was under some kind of mind - control or dark influence at that moment. Maybe he was influenced by an enemy's jutsu that made him lose his sense of self and turn on Sakura.