Ugh help

So my boyfriend. Also my soon to be Childs father. His ex wife’s bf just left her and the kids, her bf and her had been together a lil over a year and a half... my bf and I have been together almost a year and a half my 4yr old and 11 month old choose to call him dad and I’m due with his second biological child in feb... she was messaging my bf as her then bf was leaving. And now my bf and his ex wife text and conversate ALOT. I’m not usually the suspicious or jealous type, but it’s starting to make me think and wonder. When I bring it up or ask about their convo he gets defensive quickly and tells me I have nothing to worry about. They’re still legally married and I’ve told him that if he decides to work things out with her to please just tell me.. idk what to think or do.. what would you do?