Wife wants to have sex with another man

My wife has been acting strange of late she's 31, coming home late from nights out ,about 2 months ago so horny i thought she was up to something. That night i kept away from her but the next day she got on top of me and didn't stop until i came in her, she now pregnant.Thats not the problem around this time she start direct messaging a guy on twitter and having cyber sex

sorry shouldn't have posted yet..the guy on twitter told her she should have a mmf 3sum.Now i had discussed this before with her and said i wouldn't mind, so she's organised a stranger to meet us. My problem is, is this a cover?she never wanted it before ?she's very secrative of late? with her 14 years completely out of character.2kids too