To feel jealous that fiancé is studying with a female colleague who he sang praises for and said was pretty

[Quickrunner91]

My fiancé has mentioned a female colleague several times. He has spoken highly over her, saying she’s a very good woman and calling her pretty. I’ve seen him checking up on her social media before too.

Now he’s got an exam and is studying with her a few hours a day several days a week, sometimes with her, sometimes with her and a group. I feel insecure. Am I being unreasonable? I know if the tables were turned my fiancé wouldn’t like it

I can see why you would feel insecure. The pretty comment and checking her on social media wouldn't sit right with me. That said, if anything was going on, I doubt he'd openly say to you she is pretty.

The last bit answers your question.
Double standards big time.
I don't see the need to spontaneously mention she was 'pretty'!? It's not exactly a personality trait. Do you tell him you think male colleagues are handsome, then spend several hours a week alone with them?
I'm not surprised you feel insecure.

There is usually a reason why people have mentionitis.