If u have time, what does this guy mean?

So me and my male coworker. - he has a girlfriend but he has pretty much cheated on her with this other female colleague we had before she left. He said he lost feelings for her etc.
And then I had a glow up. I guess I started caring about what I looked like more and as a result got so many compliments and get treated way different now like always hit on told I’m beautiful etc. it’s actually quite sad.
But anyway he started being a specific way with me, ( when u just get the gut instinct when a guy likes you) like can’t stop smiling when speaking, constantly chatting to me, that feeling we all get when we can just tell. He wouldn’t ever mention his gf to me and posted on holidays without her in any of them. So I was just like here we go again this is the type of man he just is. He’s my friend at work but I guess it’s never really just friends with a guy and girl. Until now. He’s suddenly posted her on a day out like a great amount. Never seen before, like calling her beautiful etc and posting unnecessary couple goals type videos that people don’t usually post on their public story especially him. He’s acting obsessed with her when she looks the same is the exact same and he’s been with her for six years anyway. He posted more after I posted a picture looking nice and he just stops speaking to me outside of work in all capacity like even if it’s something you would say to a friend he’s just stopped. I know you’re probably thinking it’s a good thing and why do I care he has a girlfriend but he’s also supposed to be my friend and that’s all I wanted but I just think the energy is weird how are you going from one way to a complete other way. It just seems like spiteful or something like rubbing this gf in my face after all that time hiding her. Before, he would make up lies about who he’s meeting and going places with when I found out from other people it was his gf. How do i even act with a guy like that? Be happy for him and just be friendly like usual or stay away?