<human>: I'm F/27, he's M/27. We've been together for almost 9 years, lived together for 8.  We were best friends in high school, got together the year after. When I was younger I always said I never wanted kids or marriage but then we started dating and that all changed. He was always the type to settle down, always wanted to be a dad and a husband. I realised that all my "no marriage or kids" thing was pretty much just me being a teenager. 

We got engaged this past December, on our 100 month anniversary. I had no idea that it was this "anniversary", but these are the things he thinks about. 
Fast forward to now. He's been a bit distant lately. He's been working longer and longer hours. Hasn't said "I love you" unprompted for a while. I asked him last week what was going on. He said he was just freaking out about everything. We're currently building a house, and of course I had been thinking about wedding stuff. After he told me he was freaking out, I was upset but figured that we'd work through it. 

Then comes last night. He gets home late, I try to be upbeat about everything but just couldn't do it. I burst into tears and ask him to talk to me. Just tell me what is going on. After a bit he eventually tells me he has feelings for a girl at work. I got upset for a while, he told me he loves me and "intends on staying with me", then I went to a friend's place. 

I haven't met the girl at work, but because times are what they are, I looked her up on Facebook. She's possibly my exact opposite. Younger, prettier, very extroverted, wears tonnes of makeup, fake tan etc etc. Nothing like me. 

I don't know what to do. Thank you to anyone who bothers to read this,  I just don't know what to do. This is my entire life unravelling around me.

Could you distill the essence of the text into 1-3 sentences?
<bot>: partner of almost 9 years told me he has feelings for someone else, but he still loves me. I don't know what to do. I need some sort of advice.