I have been with my girlfriend for 4 years in October. We are both very plain sailing types, not wanting to have a drama filled life and can be very pragmatic about life and the issues that crop up. We have never argued. In July this year, my girlfriend became a little distant, quiet, perhaps a little cold towards me. I let this go for a month or so, gently asking if everything was ok and receiving the same "i'm fine" response. With Covid etc i put it down to general life strains and stress as my girlfriend was off work for 3 months. Eventually I'd had enough and decided to read messages on her phone which I don't like doing but felt I was owed an answer and knew she would have texted friends. There were messages to her best friend explaining that she felt unsure on our future but no real detail. I have approached her again about her distance etc, this time not letting her get away with a simple "i'm fine" She has explained that she felt funny about us, unsure but couldn't pin point it to anything in particular.
She is a teacher and was due a 6 week summer holiday and as we live together, i recommended she took a few weeks at her family home to get some perspective.
At about this point I have continued to read messages (which she didn't/doesn't know about) and found that she'd told a male colleague at work that she had feelings for him and he had rejected her. I had always known there was an attraction between her and this colleague although she had never confirmed this.
The summer holiday has been great, although we did have to put our dog down sadly. But relationship wise we have been back to normal, we had a bit of a break, then 4 weeks of fun and relaxed time enjoying a camping trip together for over a week in the middle of nowhere.
Everything felt back to the way it had been and I just assumed that the rejection from her colleague and the lack of school stress had given her some time to think and she'd decided she wanted to work on our relationship and it was working.
She has now gone back to school for the past 4 weeks and openly states school has been stressful. Then all of a sudden she states she is feeling funny again but can't say any more than that. I just don't know how long you fight for something before accepting defeat. We have lovely times together and I love her. I had assumed our future together was solid and set with my intentions on asking her to marry me this autumn/winter. I am looking for advice on the best course of action. If I force her to be honest about her colleague in admitting i've read her messages, it will probably end the relationship, a very much make or break conversation because of our personalities. I would like to work it through but don't know the best course of action to take.