Husband had an emotional affair with a work colleague for ~9 months. He is adamant that it was emotional only and I have seen all the (many, many) messages between them and there is no hint that it was more than emotional. She (mostly) initiated it.
It fell apart spectacularly when he told her he wanted to stay married to me, she decided she'd had enough and got (properly) involved with another man who left his wife for her. She has a history of being obsessed with people / projects, then getting bored, dumping them and never returning. There is no danger of the relationship with my DH continuing as they fell out so acrimoniously (think sueing each other). DH changed employer as soon as the relationship fell apart.
Over the course of 1-1.5 years while this was happening, DH was telling his mother lots of inappropriate details about our marriage and family life, including by messaging on his phone. I've read the messages. She spent this time urging him to leave me (he didn't, but he also didn't draw any real boundaries with his DM about talking to him about it). After me getting quite upset about this, he tells me he no longer tells them details about our relationship and I believe him.
DH and I are still together and working through the issues involved. Is it reasonable for me to expect that he would give me access to his phone in the interests of transparency and honesty?