Hi,
First, I am sorry for what you are going through
There are a few steps that you should follow in order to see this person less on your device.
1) Most importantly: Make sure this person doesn't have access to any of your devices, nor your Apple ID. Change your passwords and reset TouchID/FaceID if necessary, and log out of any device you do not own. We never know what an ex partner can do with our data (you should do that with any services or platforms you shared with this person in the past, but I would say that access to your Apple devices/Apple ID is especially sensitive)
2) Make sure you disable all sharing features (Family sharing, location sharing, shared lists, Apple Watch activity sharing, home sharing, shared notes, albums, etc.) and system features (recovery contact, legacy contact, emergency contact)
3) In Photos, if you search for the person's name, you can ask to suggest this person less often. In your Photos Memories, you can also ask for this person to be featured in less memories. You can also either delete all pictures of this person, or move them in the hidden folder or to an external drive
4) Remove any mention of this person as your partner in your and their contact card, unpin the conversation with them in iMessages. You might want to delete their contact card and any chat with them or block this person, I guess it depends how you feel about that.
Just keep in mind that iOS is a complex and multi-layered platform, you might see this person's name for a while, but if you gradually delete, hide or disable features or content related to them, you will see less and less their name showing up on your iPhone.
