Bruh

ikr he's srsly so fckn dumb it's makin me mad

I'm hoping he's pretending to not know bc he doesn't want to think about what happened on the island with Isaac but he seems so genuinely dumb to it, I can't tell

It’s cause he’s a blonde guys

The novel goes into it in more detail but Felix had some trauma and cannot remember things well. He fell for Isaac 4 years ago but he could only remember he had dark hair and average build. He has only been dating Isaac lookalikes all this time.
Now why would he, thinking he fell for some random guy at a flower shop jump to the conclusion that he was the one? Isaac could just as easily had benji with a blonde blue eyed woman? You are a reader, you have 3rd person omniscient pov, Felix doesn't have that advantage.

Cole mistook Felix word that benji was his son to mean it was his biological son....Felix meant he would adopt benji if Isaac accepted him. Unfortunately Cole realized that Isaac must be a recessive omega like his father before him. It's really, really bad news for Isaac.