Sexting

My boyfriend said I could use his old phone as a camera because my phone camera is trash. So I tried to log into my Facebook to send myself the photos but the phone automatically logged into my boyfriends Facebook. I thought ok so I'll send them over on messenger to me. Find he's been messaging someone flirting, all the photos have been deleted but it said things like "send me a pic to wank to'. Videos ect, been messaging for a while. One of them said how excited he'll be when he gets her alone in a hotel room. We have a toddler and a 7 month old. This is enough for me to leave him BUT what about the kids? He's also never changed a nappy, gave the baby food, changed babies clothes, bathed him so I'd be worried to leave baby with him if that makes sense. He was going to give baby a chicken nugget a few weeks ago so things like that worry me.