Could a person be in love with two people at the same time?

Ok, so here's my opinion.  Possibly very unromantic for an aspiring romance writer.

I think love is a decision.  That first awareness/prick of interest in someone else is probably more curiosity to get to know that person better and an acknowledgement you like what you see (lust if you want).  The better you get to know them, and the more you like them, the more you fall in love (the opposite is also true, the more you don't like them, the less likely it is you'll fall in love).  Emotions are definitely involved, but I think we don't give enough credit to the conscious decision that's being made to love another person.  When you fall out of love (or, as I'd like to think, when you decide you don't love someone anymore), it will still hurt, but it's still a decision.

Personally, I've hit really low lows in my marriage at times (luckily, not often).  But despite that, I decided it was worthwhile to work it out than give up.  Lust isn't nearly strong enough to overcome storms like that.  Speaking of lust, you also need that spark to keep things going, but you need more than that.  Sometimes you decide not to go on depending on your principles and beliefs.  For the same, the other person in the relationship could also decide to give up.  And for love to work, it needs to come from both sides.  One person's love isn't enough.

So I guess people could (decide to) love more than one person at a time.  And as Janet said, you eventually have to do something about it, it's not sustainable.  Someone is going to get hurt, if not all involved.

And for sure, you can lust after quite a few persons at a time (so I've heard, I'm too tired and don't have near enough time!). 

But I think as with everything else, it's different for each person.

This is absolutely based on romantic love.  Love for your kids, pets, parents etc. is different.