Summary: It was as if their blood calls for one another. Or according to Simmons it could just be the drug.
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Initial Symptoms
Nobody yet noticed Coulson's newly discovered love for etching inexplicable alien formulas on the wall. But they definitely noticed Skye's illness. It began with a mild fever, which she ignored as she set about securing what technological resources they do have. Then, it got worse. They all thought she had flu. It was not inconceivable for your body to break down under severe stress after all. Then her fever got higher, Simmons did all that she could to bring it down. She tested Skye for illnesses but there was nothing in her urine or stool samples and her physical examinations that are out of the ordinary. Her most recent blood sample however shows an increased cellular activity that goes way above the ordinary. Yet, there was nothing she could find that could have caused it.
Touch
Skye was convulsing and everyone watched helplessly as she did so. Coulson approached her bedside and held her hand. Only then did her convulsing gradually ceased. Simmons was foremost and observed. She approached Skye and noticed that her fever was going down. Everyone in the room was looking at her quizzically. Coulson let Skye's hand go and almost instantaneously there was a noticeable increase in Skye's temperature, according to the monitor. "Sir, I think you need to keep your hands on hers." Simmons noted. Coulson nodded. "I think it's the drug. She must be having a reaction. I wonder..." Simmons trailed off as Coulson chose to ignore her statement. Koenig got a chair for Coulson so he could sit beside the patient. Simmons ushered most of the room's occupants to go about their ways. She had been very very tired. Fitz was still not doing well and now Skye. She just don't have the energy to talk to Coulson about what they've all just seen.
A Doctor's Prescription
The only effect of sleeping in an uncomfortable arm chair while holding Skye's hand for Coulson was that it removed THAT compulsion. One that he still won't talk about even to himself. Skye's vitals were completely normal come morning. She was even well enough to announce that she wants to eat with everyone else around lunch time. As they sat eating their lunch Jemma suddenly spoke and interrupted Agent Triplet's story. "Agent Coulson, sir, I really think you should just touch Skye's skin at least once in a while until we can ascertain as to what happened. I rather hope that this scenario won't happen again but it just might. Everyone turned to look at Simmons as if she grew another head. "I really think it was his touch that healed her. I don't know what it is since I just can't see any trace of the GH 325 in Skye's or Agent Coulson's blood but I think she needs it so she won't get that sick again." Simmons continued and Coulson acknowledge what she said with a nod.
Kisses
After Simmon's 'prescription' Coulson would seek out Skye before she goes to bed or after a particularly long mission (they figured that a day's separation does not really affect Skye that much but Simmons wanted to be on the safe side) to hold her hand. He once even teased her that maybe he should tuck her in and sing her a lullaby or tell her a fairy tale. She would hug him or kiss his cheek before he leaves as her way of thank you. He turned wrongly one night and one of those friendly kisses on his cheek became a peck on his lips. Then, before he could stop himself he held her face between his hands and kissed her tenderly and left just before she could reject or return his kiss or ask any questions. The next night, Skye locked the door (they usually just close it but it was the first time it was locked during their nightly rituals) and kissed him before he could say anything. The kiss deepened and somehow Coulson ended up with Skye on his lap on top of her bed. Skye touched Coulson's cheek and bade him good night. He smiled and bade her one as well.
Complication
Skye, Agent May and Agent Triplett took close to two weeks before they could go back to the Playground after their mission. May kept looking at Skye worriedly. She knew that Skye was off. She immediately looked for Coulson to help them out with Skye as soon as they arrived but he was not in the Playground as he was needed elsewhere. Skye's fever was starting to rise when Coulson got back. Coulson immediate kissed Skye's lips who recovered as Coulson held her in his arms. Sure, May was jealous but she couldn't grudge Skye being loved by the man she loved and if the two were kept apart, it would literally kill the girl.
Simplicity
It seems that Skye was absolutely taken by Coulson. Who wouldn't be? He gave her a ride on his flying car, saved her from capture using the same and of course it was because of him that her life turned from your usual homeless vagrant to a secret agent, albeit an agent of a now defunct organization. Wrong, it's not defunct. Said man who saved her life twice is rebuilding that same said organization from scratch. Coulson was smitten with the girl too, he could even say that he was in most probability in love with her but to say that he is a hundred percent sure that he is would be a lie. He still has his issues, he also feels he's going crazy (she lessens the symptoms as much as he does hers, but he's not saying a word of course). It is with certainty however that he is fast falling in love with her. But it could also just be the enforced proximity. Or according to Simmons it could just be the drug.