We are lost in our understanding of what condition is worse.
Sexual activity with someone else is ‘worse’ because it could be avoided by simple willfull fidelity.
Loving someone else is ‘worse’ because it is beyonde the ability of the person to simply not love that somebody else.
One is worse because it can be avoided, the other because it can’t be remidied.
I think what is really worst. The true betrayal is pretending to love someone you don’t, or pretending not to love someone you do. As these are betrayals both to yourself and your partner.