🙂  I believe you can be in love with more than one person at a time, just as you can love more than one child at a time!  You don't stop loving your first child because you have a second!  Same as being in love with a partner, just because you love someone doesn't mean you can't love someone else.

But I don't think you need to even have feelings for other people in an open relationship, probably less complicated if you don't.

But it's perfectly normal to be attracted physically to other people when you are in a relationship.  It doesn't mean you don't love each other.  It's just human nature.  And if you are both ok with those feelings being acted upon, so what?  As long as everyone is open and honest about it, no one gets hurt.

Use condoms!