Unknown ending...

Hi, I'm new here. But i think i need to get other people's opinion on my issue. My partner and I have been together for almost 10 years now. Evertyhing was good until early this year. We run a small business and we only have around 2 staff at one time. Starting end of last year we hired a young girl age 18, she was nice and cute and my partner fell for her. At first he told me he only pity her because her mom left her when she was 10 yo. But later the feeling turned to be something else. He texted her almost everynight and when i confront him he told me it was nothing. And this year my anxiety and depression worsen. I cried almost everyday and he knew it but he said he can't control his feeling which i think is bullshit. Until certain time, due to an issue with her family, she asked for umpaid leave for quite some time. Even when they are not seeing each other the texting keep going on between them. This was in March. Later i gave him 2 option, choose her and leave the business or forget her and still run business together. She chose to stay and i knew he still can't forget her. The texting getting lesser but he keep posting stories showing her his routing or any update and i knew he purposedly updating stories in IG for her to see it and vice versa. But i just let it be.. Until about 1 month ago, we had quite a big argument and he started sleeping next room. We still communicate but seem awkward and most of the issues are ignored. We are just like housemate. I still keep the house clean and still cook or ordered for him. It was like habit. At work we tried to act normal and i'm not even sure wether it was an act or not. When at home, after came back, he went straight to his room and lock the door. Mostly no more small chit chat and of course no more sex. So the day before, i asked him what are we? If we countinue this relationship then i can try to live like before. But he answered he still have 25% feeling for the girl. I am devastated, shocked and mixed feeling. I cried again in my room and doesnt respond to anything and avoid the topic the next morning. He said he still trying to forget her but i don't know. He keep saying my downside is my temper. But other than that none. I can handle his laziness and bad time management and need to handle his baby-like behaviour but cannot handle my temper. Its not like i keep getting mad for no reason and this become issue when she knew the girl. By the way, I am 36 this year and he's 34 and we don't have kids. I am desperate to know what should i do. I feel hopeless and empty... Thank you guys