No. Your guarantee only covers your share of the rent, so your co-tenant doesn't need to use The Student Guarantor.
Your co-tenant can choose any guarantor they prefer. If they'd also like to use us, they'll need to apply separately with their own application. Having everyone on the same service can keep paperwork and communication with the landlord simpler.
To get started, your co-tenant can apply at https://thestudentguarantor.com/