yes, they can~ it's called polyamory, and it's been around for hundreds of years.
that said, it's pretty uncommon and most people just use it as an excuse to sleep around. or they mistake infatuation/sexual attraction for love, or their choice is mired in some sort of religious or patriarchal ideology a la sister wives.
I can't speak for anyone but myself. I can, however, say that I have loved more than one man in my life. And at times I have loved more than one at a time and have been forced to choose between them. So I most definitely can. Not sure about other people. We all have our own ideals and theories about what love is.
NOPE! I think that's full of bullshit just like the bachelor and how Ben "loved" both Lauren and Jojo. You can have heavy interest in two people maybe if you are in a really hard spot somehow but loving someone means they are the most important person in the world and you would die for them. if someone was to feel like this then I would tell them to rethink their life and maybe read about what "love" really is.