AIBU in thinking they are up to something?

[Spaghettihoops23]

Husband had a female friend from back in school days. Got back in touch recently. She's due to be married but keeps having arguments with her fiance so wedding is constantly called off then on again. DH always helping her deal with things etc. I get jealous. They have slept together when much younger-16 I think. He says no feelings etc she's like a sister.
I've hung out with her and she's really nice but just worried I'm getting the cunt taking out of me. DH isn't the type to cheat but fuck knows!
Today he went to see her to discuss the issues she has wi her mum ie wedding but obviously this now includes the fallout with her fiance!
Just got texts in quick succession saying he had to take her to hospital cause she cut her hand washing a glass. I replied then nothing. Tried to phone him, nothing.
Don't know what to think!

A few of my best friends are men. One has been going through a tough time recently and I've been helping him a lot. My DH has been fine with it BUT we have always been friends and DH knows him well.....if she's just appeared recently this may be a bit more of a red flag but you say you know her family etc. He is married, she has a fiancé (even if their relationship is rocky this still doesn't mean anything) I'd be inclined to step back and just see if anything suspicious comes up but it could be that he is just being a very good friend.