I’m not sure if she’s right that she could be happier. Neither does she. But it’s the dilemma of long term relationships. People who don’t want to be single long for the stability and security of commitment. But achieving such things requires an absence of drama, and even passion. As another friend once said to me, “you can’t have everything, where would you put it?”
Falling passionately in love is thrilling. You’re energised and glowing, the sex is glorious and you can’t wipe the smile off your face or keep your hands off each other. But love at that intensity can’t last.