My girl is a flirt

Hi Eve Magazine,

Please assist me.I have been staying with my girlfriend for 2 years now.
During December holidays I began building a house without her knowledge, my intention was to surprise her when it is completed. All did not go as planned she learnt about the project and it did not go well with her, ever since then she has been flirting with a workmate which is not going on well with me. They converse until late in the night exchanging suggestive text messages and pictures and videos.
I used some of her money in the project but I returned the money back to her.
Now our relationship is shaky, the house has not been completed and she is not showing signs of stopping the flirting.
Advise me please should I move out of our house, should I demolish the house to save our shaky relationship or should I call off the relationship? And did I do something wrong by building without her knowledge?

Please help/advice.