Husband vowing to another woman

Call me shitty for looking at my husband Facebook messenger messages. But I saw him asking a single female friend "if things happen in the future, because we cant plan it, will we be eachothers number 1" .....i dont even know how to digest this. I also saw messages of him comforting her talking about how he used to have feelings for her back in the day and he is happy she is in his life.... He put her in his restricted messages area and Idk if im reading to much into this but I feel like he crapped on our relationship hard and idk if this is fixable. I want to immediately yell at him and show him what i saw but we have 3 babies together. What would you guys do?? And advie? I dont want to jump to divorce but I will if i need too