My mother thinks my dad is having an affair with this lady who is a work college ish

She thinks he’s cheating because this lady calls him about ten times a day and have nick names for each other and they go out for lunch often

Today my dad came home from a lunch with her (they went to lunch for 5 hours) and I found her clothing in the back seat of her car....... I thought I was mine but it was a size 12 and I’m not a size 12 and neither is my mum

Maybe I am over reacting about finding her clothes?

I’m 16 btw

Update: sorry it was a jacket