You can use PartOf.
[Unit]
After=foo.service
Requires=foo.service
PartOf=foo.service
From the systemd.unit man page:
PartOf=
Configures dependencies similar to Requires=, but limited to stopping and restarting of units. When systemd stops or restarts the units listed here, the action is propagated to this unit. Note that this is a one-way dependency — changes to this unit do not affect the listed units.