Complicated to discuss because we don’t really use the same words to mean exactly the same thing.
For me, “in love”, and the falling into the state thereof, is a term for the combination of loving someone and also having sexual chemistry with them, in such a way that you get this really intense emotional high; they become the center of your universe, you glow and float around sighing and your eating and sleeping patterns change and you’re deliriously happy nearly all the time and the person you feel these feelings towards is the grooviest most delicious most adorable and brilliant and fascinating person ever to walk the face of the earth and you’d do anything to make them happy.
Then there’s “love”, minus the “in” part, which is a much more enduring and deep-seated caring for another person, a cherishing of them for the wonderful individual that they are; you’d do anything to make them happy, too, but it’s different… not without a whole lot of overlap (there definitely is) but when you’re “in love” you’d do anything to make them feel happy now, you wish to pleasure them emotionally and bring them joy, whereas when you “love” someone you may occasionally find yourself making a different assessment of what will make them happy than they may make for themselves at this particular moment; also you take your own happiness as their partner into consideration to a greater extent, realizing that if you sacrifice too much of yourself you will not, in the long run, be a very pleasant partner to your loved one, who will then be less happy overall.
Thirdly, there is sexual chemistry by itself, what I think Anaamika in post #15 may be referring to as “the physical emotions”. Or perhaps not. I’m distinguishing sexual chemistry from “in love” although it seems to be a necessary component of “in love” because the sexual chemistry can definitely be present by itself without the corollary emotional intensity and devotion and floating-on-clouds ecstasy. Sexual chemistry gives you erotic obsessions and appetites and fascinations but by itself doesn’t tend to lead you to view the other person as the finest example of the species ever to trod the earth.
All this is just terminology. I haven’t even gotten to the freaking question yet. And I’m going to use quotation marks below, but not to distance myself from the ideas as if I don’t beieve in them, but to reinforce the fact that they are phrases and that I’m using them specifically as I’ve defined them above, OK?
I’m polyamorous (as I’ve said so often that some folks complain about how often I mention it). I can tell you from experience that some people (myself included) can love multiple people and maintain ongoing romantic relationships with them simultaneously.
Being “in love” —with that intense emotional high— with more than one person at the same time?? Far less certain. I’ve never had that occur.
I can tell you that feeling that feeling does not preclude being a good loving partner to your other partners with whom you have ongoing relationships. Being “in love” is temporary, it’s partly chemical (the way it afects your sleep and eating patterns is a pretty strong clue there) and it’s seriously fantastic, the bestest of feelings ever, but let’s be blunt, it’s not a direct by-product of the sheer wonderfulness of the other person, no matter how much it feels that way to you at the time. If you’re lucky enough to fall in love with someone who is indeed an incredibly wonderful person, that person will still be someone you’ll be happy to be with once the “in love” ecstasy fireworks fade back to normal emotional hue ranges. In the polyamory world, the term “in love” (as I’m using it here) is often replaced with “new relationship energy”, abbreviated NRE. NRE is wonderful, but “love”, the other form, is what keeps relationships anchored and solid.