Broken Trust Really Sucks

My bf and I have been down a rocky ass road with trust issues. I've caught him lying, hanging out with an old "friend" that he used to have an affair with while he was with his ex, told me wasnt talking to her and I found out that they still were multiple times (and maybe even are but I haven't found any recent evidence), he cheated on me via text with an ex and I've called him out on calling other girls baby in messages... we've argued over this for awhile. He knows I don't trust him and I tell him I still think he is talking to this friend and being flirty with his ex's and girls online. He keeps his phone locked so tightly and changes his passcode frequently. He used to have a fingerprint but when I noticed he took it off and only uses the pattern now, I got super suspicious.... again. Mainly because I've gotten into his phone while he was sleeping once with his finger and he never unlocks it in front of me w/ the pattern and if he does see that I saw it, its changed or it doesn't work when I try it. I've told him over & over again that I've allowed him to hurt me, lie to me, deceive me, & cheat on me more than I have ever allowed anyone in my life. He knows where I stand on finding out hes talking/flirting with another woman that I'm done for good.

This situation isn't all easy to just up and leave. He has kids from a previous relationship (which has also been an issue) and I've bonded very strongly with both of them (9 & 2). It breaks my heart to a million pieces thinking about losing him and these kids that I love so very much.

Tonight, while he was passed out and after I put the youngest to sleep... I grabbed his phone and was determined to get in it.... and I did. I saw that he added a new contact, Mayra and that she called on his WhatsApp on 1/14 @ 6:11am, nothing else. I noticed also on his app a convo with Amber that had a smiley face but when I opened it, it was empty and then it disappeared. Amber he had an online affair with while he was with his ex. I know his history and I know he cheated a lot on his ex, the mother of his kids (they also had an off/on relationship for 9-10yrs).

I feel like an idiot for staying but my stupid heart wants to believe I'm just being paranoid but my head is over it and wants to move on. Idk what to think anymore. He deletes so much and is so secretive I cant stand it. I've talked to him about it and he says he understands why I think this way and that I'll always think this way. My logic is that if he isn't hiding anything, then why is he hiding so much and what is he hiding. Why does he delete everything. He also swears up and down that he isn't cheating or doing anything I'm accusing him of. I want so badly to believe him but I won't allow myself to.

I wish I had my phone so I could've taken a picture of his WhatsApp for my proof. Yes, I have a secure folder with all my evidence. Things we've fought about. I'm the kind if person that'll confront you right away with anything.... so its killing me not to ask him who the fuck is Mayra and why is he still talking to his past affairs. But if I do he'll know I got into his phone and boom pattern changed and probably fingerprint again. I want him to think I know nothing so I can catch him if he truly is being sneaky and unfaithful.

Idk girls, I feel like I'm going to have to break my own heart deeply on this one. I'm not just losing him but his kids and his family. They've been so welcoming and loving and call me their daughter/sister/mommy (the youngest 2yr). It's not easy walking away from this.

My brain is swimming with suspicions and it's making me go mad. I can't talk to him because it won't really do anything but cause issues. Idk what to.