My(41f) husband(52m) has a second family on the side

I’ve been sitting with this information for almost two weeks now and I still don’t know how to proceed. My husband has been in what seems like a committed relationship with another woman and he’s playing happy families with her and her three sons. They’re even planning on a having a baby. A week ago I stumbled on a tiktok account of this lady sharing her recipes and in the background I recognized my husband’s back. I wasn’t too sure at first but after taking a real good look and as his wife I know that fools neck, back,legs and the clothing he was wearing, so I went looking through her posted videos just to piece together a confirmation of it really being my husband and I continued to keep an eye on him and his movements but he seemed normal. It’s clear to me now that he has his cheating down to a science. Every time he went on his work trips she’d post these videos saying she’s cooking a new recipe because her man is coming back from his work trip. She’d plate the food up and I’d recognized his grubby hands by their look and the way he’d hold the cutlery (he has a peculiar way of holding it, kind of looks like a neanderthal discovering forks and knifes )

I can’t believe this bastard has been with her for three years. I don’t know how he found the time to start an entire relationship on the side. I thought we were happy. He tells me loves me all the time. Always brings me a gift from his work trips. When he’s home we have a great sex life and pretty much have sex four to six times a week. We talk all the time. We’ve been married for twenty one years and we have two daughters. We lost our eldest son 10 years ago but we worked through it and got closer then ever before. We are even due to have our twenty second anniversary and it’s his turn to plan it (we alternate who plans the anniversary each year). I know he’s been planning an elaborate party for us. So why is he cheating? I am so angry and don’t know what steps to take. I am utterly distraught. I thought we were happy. I thought he loved our little life.

I feel like I can’t think and I barely know where to start. I can barely focus. What do I do and how do I do it? I love coming on here and reading things and giving advice but now that it’s me I feel like I can’t think. I nearly burned my kitchen down because I literally spaced out and forgot that I was cooking.