I'll list any of the closest ones I can find. All of these are taken from the book "Japanese Idioms" by Nobuo Akiyama and Carol Akiyama. To devote oneself to someone, lit. to be kind to someone: shinmi ni naru, as in "Kanojo ga byooki ni natta node, shinmi ni natte sewa shimashita." or "Because my girlfriend became ill, I devoted my time to taking care of her." With intense devotion, lit. by forgoing food and sleep: shinshoku o wasurete, as in "Kanojo wa shinshoku o wasurete, kodomo o kanbyoo shimashita." or "With intense devotion, she took care of her sick child." To be desperate (for help), lit. to even cling to a straw: wara nimo sugaru, as in "Saifu o otoshite, wara nimo sugaru omoi de michi de shiranai hito ni basudai o tanomimashita." or "Because I lost my wallet, I was desperate enough to ask a stranger in the street for bus fare." (I think that if you took out the "Because.... and just said that one person is desperate to another, this may give the meaning you're looking for.) To use someone, to exploit someone, lit. to use someone for stock: dashi ni tsukau, as in "Kanojo wa, paatonaa o dashi ni tsukatte mokuteki o togemashita." or "She achieved her goal by exploiting her partner." (This one could also work, I think?) To exploit someone totally, lit. to even suck someone's bones: hone made shaburu, as in "Kare wa kanojo no hone made shabutta ato, betsu no josei to kekkon shimashita." or "After totally exploiting her, he married another woman." Spineless, lit. Having no bones: honenashi, as in "Kare wa honenashi de, iza to iu toki niwa yaku na tachimasen." or "Since he's spineless, he isn't effective in a crisis." (Could possibly be used as in "This person is spineless to that person?) To victimize someone, lit. to make a duck of someone: kamo ni suru, as in "Kare wa shoohisha o kamo ni shite yasumono o koogaku de uritsukemashita." or "He victimized customers, selling them cheap products at high prices."

Sorry, it's not letting me use this as a reply to the comments! ^^; To devote oneself to someone, lit. to be kind to someone: shinmi ni naru, as in "Kanojo ga byooki ni natta node, shinmi ni natte sewa shimashita." or "Because my girlfriend became ill, I devoted my time to taking care of her." しんみになる as in 彼女がびょおきになった野手、しんみになってせわしました。 With intense devotion, lit. by forgoing food and sleep: shinshoku o wasurete, as in "Kanojo wa shinshoku o wasurete, kodomo o kanbyoo shimashita." or "With intense devotion, she took care of her sick child." しんしょくおわすれて as in 彼女わしんしょくおわすれて、こどもおかんびょおしました。 To be desperate (for help), lit. to even cling to a straw: wara nimo sugaru, as in "Saifu o otoshite, wara nimo sugaru omoi de michi de shiranai hito ni basudai o tanomimashita." or "Because I lost my wallet, I was desperate enough to ask a stranger in the street for bus fare." (I think that if you took out the "Because.... and just said that one person is desperate to another, this may give the meaning you're looking for.) わらにもすがる as in さいふおおとして、わらにもすがるおもいでみちでしらない人にばすだいおたのみました。 To use someone, to exploit someone, lit. to use someone for stock: dashi ni tsukau, as in "Kanojo wa, paatonaa o dashi ni tsukatte mokuteki o togemashita." or "She achieved her goal by exploiting her partner." (This one could also work, I think?) だしにつかう as in 彼女わ、ぱあとなあおだしにつかってもくてきおとげました。 To exploit someone totally, lit. to even suck someone's bones: hone made shaburu, as in "Kare wa kanojo no hone made shabutta ato, betsu no josei to kekkon shimashita." or "After totally exploiting her, he married another woman." ほねまでしゃぶる as in かれわ彼女のほねまでしゃぶったあと、べつのじょせいとけっこんしました。 Spineless, lit. Having no bones: honenashi, as in "Kare wa honenashi de, iza to iu toki niwa yaku na tachimasen." or "Since he's spineless, he isn't effective in a crisis." (Could possibly be used as in "This person is spineless to that person?) ほねなし as in かれわほねなしで、いざというときにわやくなたちません。 To victimize someone, lit. to make a duck of someone: kamo ni suru, as in "Kare wa shoohisha o kamo ni shite yasumono o koogaku de uritsukemashita." or "He victimized customers, selling them cheap products at high prices." かもにする as in かれわしょおひしゃおかもにしてやすものおこおがくでうりつけました。 I didn’t double check any of those for spelling, but I’m trying to do a few things at once, and I think 4 am qualifies as bedtime ~_^