Simplify the following text for a Grade 11 native English-speaking person.
Original: Much of his verse was based on classical mythological themes , such as Ulysses , although In Memoriam A.H.H. was written to commemorate his best friend Arthur Hallam , a fellow poet and fellow student at Trinity College , Cambridge , who was engaged to Tennyson 's sister , but died from a cerebral hemorrhage before they were married .
Simplified: Much of his verse was based on classical mythological themes , although In Memoriam A.H.H. was written to commemorate ( remember ) his best friend Arthur Hallam , a fellow poet and classmate at Trinity College , Cambridge , who was engaged to Tennyson 's sister , but died from a cerebral hemorrhage before they were married .