So I found my husband talking to a girl I went to high school with....

So I found out that my husband and this girl I’ve known for along time that I don’t like have been talking behind my back I saw it on his phone records and his Instagram and I called and confronted her and she told me she has all their conversations saved and I told her to send them to me and she said no she’d save it for a later date. And I know it was sexual I just don’t have the texts or anything to prove it and want to know how to find out. Because he told me it was about our truck which I know is a lie and on top of it we’ve been trying to have a baby so I don’t know what to do... I could use some advice