My secret work fling was fun until he proposed to his girlfriend in front of me

DEAR DEIDRE: MY secret work fling was fun for a short time, but it quickly became obvious that I needed to get away from him and our unhealthy dynamic. 

Then he stole the limelight at my leaving drinks by inviting his girlfriend and making a big public marriage proposal to her.

The sad thing is, I know it was all for my benefit, trying to provoke a reaction. 

Now I’m wondering if I should let his now fiancée know what she is letting herself in for.

I am 28 and he’s 31.