@JanetCompost
I understand completely where you are. I know you need answers. I know you have to know you're not crazy. The damage done to you has sent you well past seeing the bigger picture and what he's turned you in too.
All I can tell you is that he's a liar. This many inconsistencies don't happen in normal relationships, whether friendship, or romantic, when there is nothing to cover up.
What he's lying about, who knows. But take a moment, you've worked out that he is lying about his Christmas night out. Was he cheating? Gambling? Secret child? Even something criminal? Who knows. But he lied about his whereabouts, to his romantic partner. You know that much.
Your brain is doubling back on itself with what you are telling it cannot be true, being processed alongside his gaslighting "truth" plus a good measure that you are deranged and paranoid. This is really quite dangerous for your mental health.
You need to satisfy your brain. You need to know you aren't mad, for your own sanity, and ability to trust yourself again.
Phone the pub. Speak to a woman. Be honest. Tell her you suspect your partner of having an affair and it's consuming you. Tell her about the plates and ask if she has them. Jeez, endless women have phoned a hotel to "catch" their husband mid affair. Even turned up trying to catch them. So who gives a shit, you're phoning the pub. If she gives you the information you need to prove he was lying, then it doesn't matter finding out the lie.
Sending love, and strength. You will get through this and at some point you will find what you need to know you aren't mad. He's made you this way. From personal experience, I almost didn't care what he'd done, my peace came with the irrefutable evidence that he'd done it, and I wasn't some broken "stalking nutjob". I was right, and sane, and true, and genuine all along.
You've got this x