Can someone please help me,my father died in 2000 and I miss him so much but the thing is he treated on my mum?

and left her to marry my mums best friend.I'll never forgive my father for doing this dredfull deed,and now my mum and my so called stepmum are quite pally(friends) again.My mum is in a nursing home and all that is wrong with her is her memory is playing up.I feel my stepmum is using or playing on my mums memory to get back in with her.My father was a great man a man who I looked up to and hes done all this.Why do these things happen.Its comming near the anniversary of my dads death as he died two days before my birthday in May.