"I would sooner die in your arms than live without you in mine." - Ares
Ares and Xena are from the series Xena: Warrior Princess. Xena was a fierce warrior who gave up her life of destruction to help and protect those in need, and Ares was the God of War who resented Xena's choice to work against him. He already had his do-gooder half-brother Hercules to deal with, and did not appreciate him meddling with his most promising protégé. Though Ares did not have much to do on the show for the first few seasons - as he was seen more often on Hercules: the Legendary Journeys - he became a very important character and presence in Xena's life in the end. While never technically a couple, they had a deep bond and a shared love that Xena couldn't ignore, no matter how much she tried to fight it. Being a redeemed warlord, Xena didn't want to admit her feelings for the God of War, though she did a very poor job of hiding them most times. They had incredible chemistry together and Ares always admired Xena's ability to use his feelings for her to her advantage. Yes, they were often on different sides of issues, but they enjoyed playing with each other and respected each other as adversaries. Ares may have worn his love for Xena on his sleeve, but that didn't stop him from getting in her way and making her life more complicated. When it came down to it though, Ares really did love Xena more than anything, which he proved when he went against his family on Mount Olympus to save Xena from death, and later gave up his godhood to save her family, expecting nothing in return.
We always enjoyed Xena when she let her dark side show through, and Ares wanted nothing more than for her to embrace that part of herself that she worked so hard to keep buried. It was part of who she was just as much as the part of her that wanted to help people, and Ares was the person in her life that was able to accept both parts over time. Of course he would have preferred that she give up her new life and come back to his world completely, but his love for her really was unconditional. There was a reason why Xena spared Ares when she went on her killing spree of the Olympian Gods, and a reason why she helped him get his powers back. Xena was drawn to Ares because deep down she knew that there was no erasing her past, but she resisted time and time again to try and prove herself wrong. She did hesitate when he offered her a place by his side as a God on Olympus, but she knew that that was not the life she was meant to live.
Though Xena died at the end of the series, I don't believe that death would be the end of their story. Ares wouldn't give up on Xena that easily, and as he had his powers restored, he'd probably be able to find her in whatever underworld or afterlife she ultimately ended up in. Everyone visited the dead all the time on both Hercules and Xena, so why shouldn't that remain a valid option for allowing Ares and Xena some semblance of a future together? Now whether or not their bond would have ever blossomed into a true romance is unknown, but Ares didn't seem to be one to give up that easily. Theirs was an unconventional love story from the beginning, but a very intriguing one, and the most interesting aspect of it is that all of his plans to turn her back to the dark side ended up redeeming Ares and making him a better person, all due to Xena.
5x13: Eternal Bonds
Ares: "I am here to help you."
Xena: "That's what you said last time in Tartarus, when you tried to convince me that you loved me."
Ares: "I do." [Xena scoffs] "Ooh, I love it when you play hard to get. But that's why I'm here- to prove it to you."
Xena: "Then you're wasting my time. I'd never swallow that."
Ares: "Thanks to that kid of yours, I am dying. So why would I lie?"
Xena: "Because you're Ares, you always lie."
Ares: "Well not anymore. All I want is to end my life the way it really started - fighting side by side with you."
Xena: "You forget I fight against scum like you."
Ares: "And so will I. A fight is a fight, no matter which side you're on."
Ares: "I was kinda hoping you'd be back. I gotta know what happened. I thought you were dead."
Xena: "That's a nasty rumor."
Ares: "No, no. See, I mourned you. For years I mourned you."
Xena: "I can see you looked positively grief-stricken when I saw you today at the arena."
Ares: "What? That rough and tumble with Livia? You're not jealous."
Xena: "Of a Roman wannabe? Hardly."
Ares: "Well you're right, she's not you. Because if I thought for one moment that you being here meant we had a second chance."
Ares: "I'd drop her like a nasty habit." [they kiss]
Ares: "You're not gonna kill me are you?"
Xena: "Why ever not?"
Ares: "Because I love you. Yeah, I love you."
Athena: "You healed them without my blessing? That's impossible!"
Ares: "I gave up my immortality to save them."
Athena: [in disbelief] "Why?"
Ares: "I'm sorry, but I've got a thing for her."
6x01: Coming Home
Ares: "Mortality stinks. Not to mention hurts."
Xena: "Yeah, it does sometimes."
Ares: "You have got a wicked right-jab."
Xena: "Sorry about that." [she smiles]
Ares: "It's not the end of the world. Who knows, maybe as a mortal I can experience something I never could as a god. "
Xena: "Like what?"
Ares: "Like you."
Xena: "You never give up, do you?" [they kiss]
Ares: "Ow." [they laugh] "I guess I'm finally getting to you."
Xena: "You always got to me, but you were bad for me Ares, you still are." [she walks away]
Ares: "Xena! Is there even a chance we could be together one day? I don't know, maybe one in a thousand?"
Xena: "More like one in a billion."
Ares: "So you're saying there is a chance?" [she chuckles and smiles at him]