He doesn't feel betrayed by the events of that race ten years ago, not any more. In some fucked up way he understands Valentino, he understands why he did that. He understands why he kicked him, and even more than that he understands why he said everything he said. He didn't, not before, but now he knows what it's like to be so desperate to win one more title—to prove that you can still do it. Marc proved that he could this year, but Valentino had that opportunity ripped away from him. While Marc is still angry that Valentino never once bothered to ask him about it, and that he never wanted to hear it when Marc offered, he can't say that he doesn't understand the desperation.
But even with the new understanding that Marc has, he can't forgive Valentino. He can't forgive a man who will never apologise. Marc understands why Valentino acted how he did in 2015, but what he hasn't reconciled with (and may never manage to) is just how easy it all seemed for the Italian. He never once displayed any guilt, any sympathy for how the media turned on Marc with him. Not once, no matter where they were—alone or otherwise—did Valentino ever show anything but disinterested cruelty.