Am I right to feel upset because my daughter reached out to her biological father?

So when I was 21 I was a complete waster, made a balls of my leaving cert, stacking shelves in Dunnes and going out three times a week. Met a girl and we started going out. The week of my 22nd birthday she announces she's pregnant. My parents clearly don't think I'm mature enough for a kid but put on a happy face. For me it's the moment that forces me to sober up cop on and return to third level and get a degree. Baby is born but by the time 2 it clearly isnt working with mother so we split up. However I'm determined to keep providing for my daughter and after graduating start making decent money in IT.

Anyway fast forward daughter is 14 and she stays at my house at weekends. Very good relationship I'm very proud of her. She loves visiting granny and grandad. A few weeks before Christmas my ex, who is obsessed with family history, genealogy all that decides to do a family history DNA test from one of those online sites. Ex calls me up and nervously breaks news to me that I'm not the biological father of of my daughter. I'm shocked for about a minute but very quickly accept it. Feel no real anger towards my ex it was a very long time ago. Reassure daughter when she comes around that I love her and we share a very long hug.

Anyway last night ex calls me again telling me "not to freak out" but my daughter earlier this week reached out to who my ex thinks her biological father is on Facebook. Now I was very pissed off to start with because my ex HAD NOT told me who she thought that man could be. But it was as if before this man was an abstract, the past. But now he's in the child's life, he's her real father. I felt an intense anger and frustration. I felt humiliated in a raw way I hadn't experienced before. I'm not a super emotional person, I was very calm when I was told about the DNA test results last month. But this news somehow just floored me in an entirely different way.

Today I had to head into the office but was basically stewing over things all day. It must have shown on my face because coworker asked me if I was alright. Anyway supposed to drive down to collect girl tomorrow for weekend stay and I really want to fake some illness so I don't have to. Feeling very lost atm.