What do I do

My husband is my best friend but we’ve had our problems the past few months. He swears up and down he would never cheat on me. There’s this girl though and years ago he dated her sister. This girl is grown up now and has a boyfriend and three kids. My husband tried to give her boyfriend a job but it didn’t work out cause her boyfriend is pretty much a scum bad/drug addict. She tries to be my friend too and I tried to be hers too. But the other day I see my husbands phone and she texted him at 3 in the morning “B**** is at the bar fucked up with other girls, I wish you were here”

Then today I see a text from her in the middle of the day “When can you come over, B**** won’t be home for a while.”

Both times when I ask about it he won’t let me see him phone and just recently he put a password on it so I can only see the message when he first gets it and it displays on the lock screen. He yells at me and won’t let me see his phone then will go in another room with it for a few minutes then comes and calls me to look st the phone and shows me the message and it looks like all the messages before it were deleted.

This is bullshit he’s making me look stupid. But I don’t have solid 100% proof he’s cheating and he swears he would never do that. What the hell do I do to prove this??

***he says she’s just crazy and he thought he blocked her but like cmon?? Seems super suspicious.