Absolutely distraught so please be gentle 
Iv actually written a post before about how dps female colleague said some stuff which rang some alarm bells for me (you can search the post from my username)
Well now I went n looked at his phone and in complete shock I'm so so shocked they've been txting.
I had to check rly quick COs he was in the shower, all I saw was her saying "might have to have a biopsy would u still fancy me with one boob?"
His reply "of course I would"
Then another text from him saying when they could see each other
I was in a panic not 100% but I'm sure I saw a txt from him saying "I'd like u on top"
I just can't believe it. This is a woman who he's told me before looks old n isn't his type at all. He also said she was a HO (higher officer) n it's not good practise for flanderings with HOs. I think that was a time when I getting suspicious about her so asked
Now I'm not sure what to do. I'm in rly big shock because he's told me before she's 40 n single, wants to have kids n settle down. What hurts me the most she knows about me so how can she do this? What do I do now?
He talks about me quite a bit in work so I just can't fathom why she would consider having an affair with him when she knows he's in a long term relationship with two children
I dunno what to do. I can't confront him can i this soon? Weird thing is this week we've been rly close one of my students has committed suicide so I've been rly out of sorts n he's been there for me n basically we spend every evening together. It's not like he's been away
N if he does go away with work she doesn't go because she's a HO so now I'm wondering how did this happen/develop
Please someone help me I'm in a rly low position Iv told my friend today but she couldn't talk properly feel like I have no one to speak to right now