Leave them alone.
Stop thinking while seeing someone loving their other half with all dedication, love and respect that if you were in that place how lucky you would be.
"NO" you wouldn't be lucky because the love, respect dedication that person has for her/his other half is because he/she is the person they love. They are the people they want to spend time with and share their life with. So stop trying to get into someone's relationship just because you like the way that person loves the other. If you would be in their place you wouldn't be getting that. Because you are not the person they love.
SO STOP DOING THAT.
LEAVE THE HAPPY PEOPLE ALONE and HAPPY.