Sometimes dear Jhane,as we get to see within this world,men of this world are more committed to each other and the fleshly things of this world more than they are of God.
So the answer is Yes HEathen(unbelievers) can love one another and be very committed even to their deaths.
They will love and remain committed to each other and even forget about the Lord and God reveals this.

Matthew 5 (King James Version)
44But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you;

45That ye may be the children of your Father which is in heaven: for he maketh his sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.

46For if ye love them which love you, what reward have ye? do not even the publicans the same?

47And if ye salute your brethren only, what do ye more than others? do not even the publicans so?

48Be ye therefore perfect, even as your Father which is in heaven is perfect.

Hope this is helpful:)
God bless,love and respect