The best sign of friendship or love is how mutual is your pain, they say if your hearts bleed together then your bond is deep.
If a person is absolutely nonchalant to your pain, suffering then chances of love in background is very rare. Happiness can be ignored, because mostly its expression is very subtle, so if your friend does not dances with you all the time when you are happy that may not mean that there is no true love, he may just think you are too naïve and childish.
But if your friend does not gives a hoot to your pain, suffering, sickness, dangers you can be quite sure that there is no love in background, maybe a little fondness but not much love.
Then you can decide how much you will invest.
In my life I have often used this yardstick to identify stalkers who stalk me with ulterior motives, or hidden agendas over those who actually care for me.