Hi Cazzy how are you?
He probably was out with a woman, not his brother like he said, however your never going to know really like you said he has never introduced you.
If it's any consolation I think men (and I use that term very loosely!) like him and my ex, use women, they say all the right things we believe them because we are good people, and when they've got what they want, they're not happy and want bigger and better things, they don't care about women at all, just their own selfish needs.
Look at last night for you. You texted, phoned but he never bothered, no he wouldn't having too much fun where ever he was, but if the boot was on the other foot, and he couldn't contact you all hell would break loose.
You honestly don't need the stress, you need to put yourself first, and your kids, and get rid of him today, get his bags packed, call your brother for moral support and get rid of him, it will hurt, I'm not going to lie, but this won't last long, better a little bit of heartache now than a whole load when he brings something nasty home.