I think it's natural to be shocked but your attitude is appalling.
Many, many years ago I fell pregnant to a man I had been seeing for a couple of months. I told him and he cried like a baby. I couldn't figure out why, he said he needed time to think. I left him to get himself together and the next day I returned and his flatmate told me he had moved back to the place he came from and to his girlfriend. 
I had no clue and was gutted and felt foolish amongst many other emotions.
When baby arrived I could not put his name on the birth certificate because we were not married. I had left my contact details with his flatmate to pass on, which he said he did but I never heard from the father and I relocated for support from my family.
When my son was 4 he asked me about his dad so I told him. He said he wanted to meet him, we talked it through and I told him I would try and find him. It took weeks of phoning complete strangers with the same name in the town he originated from but I came across his mother, left a message for him to call me. A week later I rang back to see if she found him and she said she passed on the message but he didn't want to know so I was to "go away and stop causing trouble." I had to tell my little boy that I couldn't find him because I didn't want him to feel rejected again.
When he was 9 he asked me to look again. I rang up the father's mother again and this time she wanted to talk and asked me what it was about. I told her and she spoke to me for a long time. She said she would pass on my new contact information but she couldn't get involved with my son if her son forbid it. (I hadn't asked her to.) A few days later I started getting nasty, horrible phone calls from unidentified people telling me I was a whore, a slag, a scrounger, every derogatory name you could imagine. I was standing in the kitchen on one of these calls looking at my lad sitting at the table, trying to keep calm. I had this verbal abuse being drummed into my ear whilst looking at my son and thinking how he didn't deserve such nasty people in his life. They then said my son was a bastard and would never be welcome in their family, that I had to crawl back under the stone I came out of, that I was wrecking lives because people were upset my son existed. I recall hanging up and going into the bathroom for a good bloody cry. I realised then he would never have the relationship with his dad that he wanted. He was such a lovely boy when he was younger, a really good kid and very loving and I didn't want to break his heart. I had to explain to my son that it was not possible for him to meet his dad and then when he was older we had a rather more open chat about the last phone call when he asked yet again if I would help him find his dad.
I only ever wanted to facilitate my son having a relationship with his dad. I didn't want his money, my son's needs were fully met by me. The problem is now that he is a grown man and is deeply traumatised that his dad didn't want to know him, has an issue with a lack of identity and is too scared of further rejection from his father. The fact his dad never cared enough about him to put food in his mouth or clothes on his back yet ALWAYS knew about his existence really hurts my son. I discovered though the father hadn't told any of his family or his girlfriend about getting a girl pregnant until I went searching for him a few years later.
Your situation needs an adjustment in attitude OP towards the child and the mother. You really know nothing about her, only what you have managed to put together from social networking. She is not the one changing your life, your husband clearly sowed the seeds a few years ago and he is the one you should be holding responsible.
So sick of seeing this whole demonising of single mothers because she's been left holding the baby and the father has managed to wiggle out of it and keep it secret for years. THEN when she finally catches up with him he continues to abuse her by denying her, the child, any knowledge of their existence. Really shitty. It causes pain and hurt for the child which follows them into their adulthood.