It always amazes me how many of you on here automatically jump on the "he's cheating", "get rid", "check his phone" etc.
It's no wonder blokes have left you and treated you that way, clearly they feel so insecure or inferior due to your behaviour.
Everyone constantly is saying 'Be Kind', support each other, but all you'll have done is fuel a fire, that potentially is nothing, but the poor OP now thinks her partner isn't even working on a Saturday as they're meeting someone. Doesn't take a genius to figure out if he's meeting someone else, he wouldn't have text them at the same time?
I joined MN to literally check if there was anything me and my wife might need to consider for our little girl; yet it's just full of bitter twisted people half the time that resent their partners / lives. (Excluding those looking for advice on abusive relationships etc). Not all men are the monsters described.
To the OP, I hope it was just a typo that they sent to you. The most sensible thing to do would be to just ask him. He will obviously say it was a mistake, it's then up to you to decide if you trust him enough to remain.