I really appreciate all of your thoughtful questions!
I am quite in love with my boyfriend, actually. But none of that takes away from the love and commitment I have for my husband.
Think of it this way--do people stop loving or caring for their first child once they have a second? In most cases, absolutely not. So we know that people are perfectly capable of loving more than one person at a time.
Of course, having one child (like me), no children, or ten kids are all valid and based on very personal reasons for everyone. All are valid.
I seek out new relationships knowing that I have obligations (like our shared home, finances, and child) with my husband. I make that clear upfront.
I seek out partners who are not looking for a nesting partner (partner who lives with you).
My boyfriend, for example, already has a fiancé who is his primary partner. I have another partner who is "solo poly," which means he prefers to live as a single person, without combining a home, finances, etc. with any of his partners.
So falling in love with other people is a non-issue as far as that goes. I know that I can love more than one person, and my partners know that I have no desire to move in with/have kids with anyone else.