Does bondage always include pain and humiliation?
No. Some people enjoy bondage simply for the pleasure of tying up a willing participant. Japanese rope bondage can be very visually appealing, isn't painful for the person being bound, and if done privately or in the company of trusting, respectful companions, would not be humiliating. Some people get pleasure simply from the feeling of restraint and helplessness that being bound creates. And of course "bondage" isn't limited to ropes. Silk scarves have long been employed as a gentle form of bondage, and can help create a loving, caring atmosphere.

Does pain always include bondage?
No. Some scenes rely on pain-without-bondage: think of a 'teacher' bending his 'student' over his lap for a spanking, or a slave ordered to hold out her breasts so that nipple clamps can be applied. Pain brings a strong endorphin rush and can be quite exhilarating. The mere act of remaining still while receiving pain is a very submissive way of behavior and can be quite admirable.

Does humiliation always include bondage?
No. Humiliation takes many forms, the common theme of which is degradation. Licking someone's shoes clean? Degrading and humiliating. Being spit upon? Embarrassing and humiliating. Being called a filthy, worthless slut in front of a group of people ogling your naked body? Definitely humiliating - and no bondage required.

Do all three always go together?
Sometimes, but certainly not always. There are as many ways of incorporating bondage, pain, and/or humiliation into one's sexual activities as there are people in the BDSM community. Think of them as overlapping Venn diagrams - bondage only, pain only, bondage and humiliation without pain, humiliation and pain without bondage... so many possibilities, and not enough nights in a lifetime to explore them all.