It sounds like you're not married and have no kids yet (?)
You can go through s solicitor to sell the property and split any deposit (presumably no equity yet) according to what you put in. In the meantime one of you should move out, it should be him but (being what he is) he'll probably fight you and won't go. Do you have anywhere you could stay for free (family) til the house is sold as I presume you can't afford to pay your share of the mortgage and rent (?)
Ive always found aggression/anger etc to be a go to technique when people are caught out (or know they will be if the other person delves further)to get them to back off, back down, whatever. Attack is the best firm if defence and all that.
Caring the other person crazy, bitter, paranoid, won't let something go etc is another technique to get them to back off and be s good, quiet, unquestioning, lapdog who doesnt rock the boat.
His guarding of his devices, alongside your instincts, with the crucial background that you've caught him cheating (which is most definitely what they was, whether there was ever anything physical or not) .... Suggests he's at it again, or in an o.ging basis.
"Some random" is also a technique used to try to minimise and distance the cheating with the woman he was exchanging nude/sexual.pics with and no doubtt sexting (if that's all that happened). Bit like bill Clinton's famous "that woman".
I'm also puzzled at how you'd add someone you don't know/whose number you don't have on WhatsApp.
Anyway, he's cheated,looks very much like he's continuing, your instincts are spot on, you can't trust him, and it would be a disaster to get into further commitment with him.