The question of whether the new relationship will succeed relates to what function it is playing in your relationship with your current partner.
If you have the kind of primary relationship where you initially experienced a significant amount of time where you were mutually in love and satisfied with the relationship and then grew apart because of life stresses or conflict and you entered the affair to experience being in love again, this does not bode well for the long term success of the affair relationship.
Of course you should not make your decisions based on what others would think or feel.
Losing a long-term partner, even if things feel bad, is still a loss and needs to be grieved.
I came across an interesting statistic recently; 25% of relationships that start as affairs succeed.