Need advice! Should I send tell all letter

Long story short I was living with my ex and his family. I was with my ex on and off for 7 years. My ex constantly lied about things throughout but early this year I found out he had been engaging with escorts and inviting them round when I wasn’t there.

At one point before I found out, he was in the kitchen with his brothers girlfriend and he didn’t acknowledge me and because I’d always been suspicious about him and still suspected he was dabbling with escorts, my instincts were telling something was going on, nothing was going on between the two but I was picking up on something.

Anyway, one morning I sent him a text in the way she would text him with an emoji and he called her downstairs and I blurted put something ridiculous like “you were hovering around him in the kitchen” then I was made to look like the insecure, paranoid girlfriend when something WAS going on, he was engaging with escorts and sending messages for them to come round on the nights I wasn’t there.

His mum even said to me that I let my insecurities run away with me.

It irritates me that no-one knows the full truth, his mum and his family have always been on his side regardless of his actions. I have moved out now but I’m still upset by it all.

I was planning on writing the brothers girlfriend a letter with photo evidence and also to warn her that random strangers may be coming to the house she lives in with her daughter.

I think I’ll feel a lot better with the truth out instead of me looking like the insecure/paranoid girlfriend he made me out to be.

Please can someone tell me whether this is a good idea?