@sparkle420, per your updates, I’d say that he is cheating.
The changes in his behavior — cutting communication when away, blocking transparency on his phone, ignoring you when he goes out, lying about his whereabouts, taking lube on the trip/sneaking it back, putting the lipstick stained shirt into the wash — all point to infidelity. He’s out there acting like a single man.
Regarding his guff about being tempted to cheat with bar randoms while working away because of a rough patch, he was indeed throwing a bone to make you STFU. He could be cheating with strangers when away, but it’s more likely that he is having an affair with this colleague you are suspicious of, who is with him at home and on work trips. His shutting you out in general points to a local OW.
He’s primed to shift the blame for his cheating, which is bullshit. His unethical decisions are not the fault of you or your relationship. He is responsible for protecting his fidelity and being a safe partner. Instead he has created distance between you to make room for another woman/women.
@sparkle420, it sounds like you can’t do much investigating as he has now locked you out of everything. Being distressed with constant anxiety and uncertainty is no way to live. You’ve spoken to him about your discomfort, but he has failed to change his sneaky, secretive, devious ways. I wouldn’t be able to move forward with him under these circumstances, and would be speaking to a solicitor to learn what my options are.