Everyone makes nicknames for their significant other when they are in relationships. Of course, some nicknames can be cute and sweet. Depending on the nickname it can be taken too far.
When you say a certain nickname it can get annoying after a certain period of time. The period of time isn’t really calculated or determined I should say. How someone can get annoyed is by how you say it and how you mean it. Of course, you can say pookie bear but in reality it maybe not the ideal nickname that the person wants.
In the end, ask what they think of nicknames. Just generally talk about it with them. Ask them what some common nicknames and see what they think about them.
A nickname that comes from the heart is always the best solution in the end. If you do not mean it in the end then dont say it. Typically if you say it from the heart then the relationship will last longer.