"Once a couple (stop loving each other) is there any way back"
The politically correct answer is to say, "Yes if both people are willing to make the effort and get some therapy, "Real love" really never dies...etc
However the truth is "It's easier to maintain a fire than it is to reignite a spark."
Yes you can perform romantic gestures and have sex with someone you don't love. People do it all time.
To love something whether it be chocolate or another person is to "crave" or "desire" it, not being able to imagine your life without it....etc This kind of love you can't "manufacture" or follow some master plan to connect the dots and create MAGIC.
Having said all the above if you still enjoy each other's company, trust one another, and have a lot in common then maybe you can be content without "passion". The most important trait required to have a successful marriage is both people have to want the same thing and agree on how to get it.