I think this song is about someone who wishes to help someone, but it‘s not quite clear if this somebody wants the support at all. The lines start always with „I‘ll“ and not with „I could“ or at least „I want“. It seems like an obsession to me, a song about the obsession to help someone. When you listen to it, the singer appears to be some kind of stalker, who interferes into someones life. The chorus emphasizes this suggestion, because the lines „I‘ll be your father, I‘ll be your mother, I‘ll be your lover“ sound very „focused“ to me.
You could also interpret the line „Well I‘ve seen you suffer, I‘ve seen you cry the whole night through“ like a statement from somebody who observes or observed a person for some time, a typical behavior for a stalker. The whole style of writing of the song is another „evidence“ for me that the writer is somehow insane or obsessed; those poetic words that sound like taken from a mystical spell. The singer wants to sacrifice himself and be the almighty protector, the good soul that understands the problems and wants to erase them for „the victim“. He feels like a hero, the only person that is capable to „drown the demons“ and to make the person feel better again. The line „And I‘ll be your anchor you‘ll never leave“ expresses that very good, the desire of the singer to never let this person go again.
The other possiblity is that it‘s a song to soothe somebody, maybe some kind of a bedtime song, to make somebody calm down and relax. It could be a song for a person that feels or felt very lonely or desperate and somebody wants to help this person with words, in this case with chanted words. It could be that the person who sings wants to wash away all the worries of that somebody and load the burden onto himself. He wants to solve the person‘s problems and be there for him or her 24/7. The song should express those feelings and show the person that there is somebody who cares and who wants to help. The line „I‘ll be you ether, you‘ll breathe me in“ says that the singer is always available for this particular person and that he or she should „make use of him“. Another argument for that proposal is the last line of the chorus and the title of the song „I‘ll be yours“. It also shows that the singer surrenders to the suffering person, that the person „owns“ him now to get better.