The Start of A Downfall

After Lucy and Natsu have been dating for quite some time, Lucy had gone out one morning to look for the dragon slayer on her own behalf, eager to see him since he had changed his routine recently. When doing so she had caught him at a distance with they're fellow guild mate.

She witnessed a couple certain actions take place which left the celestial spirit mage in shock and torn apart. Was this epidemic the end a happy relationship between the loving couple?