MIL worried she'd be the bad kind, then her son's gf showed up and changed everything

So my son didn't even know where his girlfriend's school was, right? And I was joking like "you don't have sympathy issues do you" and he was laughing saying "yeah I do" but honestly I wasn't sure if he was serious.

Everyone says the best MIL-DIL relationship is staying distant like strangers, no daughter-like DIL, no mom-like MIL. But I promised myself I'd still treat his future wife like my own kid. And then this girl walked in. She's genuinely like my daughter. I don't have a daughter so I don't know what that mom feeling is supposed to be, and I was SO worried I'd end up being a shitty MIL. But I think I can treat her the same way I treat my son. I kept wondering if I should be like a mom to her, or just a neighbor, or distant... and now I know.

After she left the other day I asked my son why he decided to marry her. He said even now she's good to him, but those first few years? She was GENUINELY amazing. Turns out he doesn't talk about family stuff much so she thought his parents didn't even exist. That's why she took extra care of him, treated him so warm. When he finally told her he actually has parents, she said "oh good, you don't need me to help support you then" like it was a relief for him.

And now he's bragging to me about how his girlfriend has no prejudice or preconceptions. I'm grateful, I really am. But there's this weird awkward feeling sitting in my chest. Is it because I'm the MIL...?

Just be happy.