Does my girlfriend have a crush on someone else?

Hi,

I've been in a relationship with my girlfriend for almost two years, we are both 40 years old.

Over the last 6 months we've be going to the gym together to classes, roughly 5 days a week. 4 out of the 5 days a week I feel like we have fun and we're always talking and laugh at each other during the class.

On one of the classes per week my girlfriends behavior seems to change. Like I become none existent and I feel she may have a crush on the class instructor.

I just want peoples opinion on this, because its been going on for 6 months and I've not said anything because I don't want to come across as being insecure, but I need to find a way to approach this carefully and maturely.

To give you some context behind why I feel my girlfriend may have a crush on the class instructor is as follow.

1. She never wants to enter the class with me, she always wants me to go in first and she comes in a few minutes later. She tends to say "oh I just need the toilet, I'll meet you in there", even if she's already gone before we leave home.

2. The moment she enters the class, her gaze is instantly on the class instructor and it stays there for lengthy amount of time. For example at least 1 minute or so. 99% of the time the class instructor isn't aware she has come in, however on the occasions he is looking over her body language is like a school girl who has a crush (I think you get the gist of what I'm trying to say).

3. Before the class every 30 seconds or so she is constantly gazing over to him to check if he's looking.

4. During the class, she is looking over at him, again not in a way that suggests she is taking instruction on what to do, its more of a long and lengthy stares and when he looks at her she goes all smiley like a school girl on a crush again.

5. During the class when I look over at her, she sometimes looks over a me and instantly stops looking at him, but as soon as she thinks I'm not looking its back to look at the instructor.

6. During the breaks she is constantly looking over at him every chance she can get, sometimes to the point she is looking in the class mirrors just to get a glance or uses her water bottle to try and hide her glances over.

7. During breaks her entire body is constantly pointing in his direction.

8. She seems to be very disinterested in me compared to the other classes we are in which doesn't have this instructor. In the other classes she is completely different and positive towards me.

9. At the end of the sessions as we are leaving she doesn't acknowledge me at all, but looking at him at all times until she leave the room.

10. The instructor mentioned to the class that he wants to do Yoga, all of a sudden she has now started to suggest that she wants to do Yoga and has made comments about me not coming because she says I won't like it.

Sorry this is a large list, but I wanted to try and express what I am seeing during the class. Am I just being insecure as most people would suggest or with all these small little things I've noticed over a 6 month period lean towards my thought that she has a crush on him?