I believe it's possible to have feelings for two people at the same time. But not as far to say love.
If you truly loved your partner, that love would be reserved for them alone.

I'm kind of mixed on this. I think that it's possible to love two people at once but I think eventually one person will win out over the other in a sense.

What zanhar1 said.

There's different types of love that demand to be felt at different eras of a person's life. You may genuinely love someone when you are 19 based on what little you know of the world, and by the time you're 28, you're a completely different person. It doesn't invalidate what you felt before, you've just changed.

Where simultaneous love is concerned, I think that's possible too. Again, you can be passionate, fireworks, fling-like in love with someone and not want to settle down, and all the while you can meet the sweetest, cutest, dorkiest person you've ever known in your life and want to marry them right then.

my friend is dating someone and she likes a lot of people (or just 1)

I agree with Zeppie.

Happened to me recently, I only like 1 person now.

Everyone is different so I think it's possible for someone to love more than one person at once. I'm not like that myself in the slightest, so I can't say one way or the other how that actually works in practice, but I imagine some people genuinely work like that.

I have no idea. Probably.

The universe has a sick sense of humor....

absolutly! though I totally understand it's not for everyone!

I don't see why it wouldn't be possible.

That depends on what you mean. If you're referring to romance, I think so. I've never experienced this personally, but I think it's possible. But as for crushes, also yes, as I have seen it happen with a friend of mine.