He didn't send his friend to collect him. He was in the car with the friend, and the friend walked over to avoid conflict. Your title is very misleading, and makes it sound like he just wasn't there at all.
I know you're hurting at the moment, it's all very raw, and you feel you've been treated badly.
There are three versions of what happened - yours, his, and the actual truth, which usually lies somewhere in the middle.
If he has cheated, that's awful. You can't control his narrative to people he knows, though. It's wrong to lie, but obviously he's not going to want to admit to people what he's done.
What you CAN do, however, is deal with things as best you can for your son, and try your absolute best not to get bogged down with every last thing.
Your husband did see your son. That's what's important. Not who physically walked out of the car. You can't control how he parents on his time. That's a lesson that you need to learn quickly now you're separated, and it can definitely be frustrating and difficult!