Different cultures have different takes but greek and Latin define different forms of love. From impulsive maddening love (why cupids arrow was seen so harmful) to dutiful love (the kind made through obligations made through shared commitments and aspirations) to brotherly love (trauma bonds, solidarity, commitment made from shared respect).
There is also paternalistic love formed from empathy and a desire to protect. And of course love to describe the deep joy something gives you and desire to have it again.
When they ask "do you love her?" Based on the context I assume either or both love as a desire for the other or dutiful love, because both can be consuming for many and mean they would struggle to have that the capacity to share that same level of love with their current partner.
If they don't and it was an act of lust* or curiosity then they're partner may feel more comfortable with the commitment to them.
impulsive love and desire can be heavily intertwined with sexual desire but that is a whole other interesting discussion to me