I think it differs for everyone, depending on what your concept of marriage is, what your goals are for it. Do you want to be in love with someone versus do you have to have a loving relationship/partnership only.

That's so subjective. What does "no longer in love mean?" If it means the fireworks are gone after 20 years, well, yes, that's probably going to happen.

My parents, who love and respect one another dearly, often remind me that marriage is work. Some days it's much harder than others to like, let alone love, your partner. My question to you, I suppose, is whether you really truly feel that you and your husband have grown so far apart that you can't find your way back to one another.

Are you really "out of love?" Or maybe just "out of touch?" Do you want to try and work it out? If you feel that this person is still someone you deeply care about and want in your day-to-day life, then maybe the answer is yes.