I fixed the schema as best I could given I don't know anything about your process. I removed the duplicated fields so they appear in only one table. Since you seem to want the allocations to be viewed in datasheet form, I made the remarks a separate subform. As you click on a new row in the allocations table, the relevant remarks will show in the remarks table. If you prefer the remarks to be a popup, that's fine but I prefer this view since everything seems to fit.
Three things are required to sync the two subforms.
1. The recordsource query of the remarks subform uses criteria that references the PK of the allocation subform.
2. When the current event runs for the allocations subform, the code requeries the remarks subform to activate the new key value.
3. When adding a new remark, the BeforeInsert event is used to populate the foreign key that links the allocation and remarks tables.