I SAW MY DAD MAKING LOVE TO OUR MAID,SHOULD I TELL MY MUM?

Am a 17 year old girl that just finished writing the WAEC and NECO exams.One day,My Dad thought I had gone to school as usual for my exams,but i just finished writing exams the pevious day,so I had to take a long rest to relieve myself for all the exam stress i had gone through.My Dad has a business of his own,while my Mum works as a physiotherapist in a Government hospital.It is a usual routine that my Mum takes us children to school every morning.
It was 12noon when i started hearing some strange voices in the parlour.I never expected anybody to be at home at this time other than our maid,but the voices i was hearing looks like my Dad`s.My room is very close to the parlour and you can virtually see everything that goes on there.I peeped in through my room door and guess what I saw,My Dad on top of our maid making passionate love to each other.From what I saw,they have been on this for a while and to my utmost suprise,I overheard our maid calling my Dad by his first name.I hated my Dad for this action.It`s been over a week now that this incident happened,both of them never knew I saw them.But I can`t take this any longer,Please advice me,should I tell my mum?