Found out the man I’m seeing is having a baby

Hi everyone, just seeking a bit of advise with how to proceed with the situation. I have been seeing this man since mid September and we have been getting along just fine. He has 2 kids with 2 other women and one of them he is really close with. I have asked him many times about the situation between them and each and every time he has reassured that they are not together and haven’t got any relations, just remained good friends cause of their daughter. Last night while scrolling on tiktok I came across a video of a woman posting her gender reveal from late October and I see him with their daughter. And upon looking through their account, they are very much together and expecting another child in March, meaning that she was pregnant the whole time he was seeing me. I have not yet told him that I have found out and I will obviously no longer want to see him and feel really horrible about the whole situation but not sure how to proceed? Do I confront him? Do I contact her and tell her?