I, Too, Have Suffered in the Garden by Jennifer Hritz

Still suffering the fallout of his partner's death from AIDS a dozen 
years ago, Adam Atwater tailspins after his fortieth birthday as he 
copes with his father's terminal illness, a career from which he derives 
little satisfaction, and an affair with a colleague that leaves him further 
from his current partner than he ever imagined. As Adam cares for his 
father, memories of Bobby's illness resurface, along with guilt for the 
infidelity he incurred as his lover lay dying. Tormented by the past, 
Adam teeters on the brink of insanity, poised to lose everything he 
now holds dear.