Sam didn't want her to leave again. He relied on her too much and had forgotten what it felt like to be as lost as he had been without her around. Between her and Faith. Sam almost felt like he had after Dean's death. That wasn't a pleasant feeling at all.
"Castiel is generally confusing," Sam pointed out, looking a tiny bit amused. "I'm not surprised that he makes you feel that way. But the love thing? I think you need to hang onto that, Ruby. People don't get to fall in love a lot, you know. Not really." Sam had been lucky enough to go at it three times around himself. All love, all different kinds. Each time it was different. Each time it was special. Sam was actually very glad that Ruby was given the chance to experience it. Love was important. And as far as Sam was concerned, she deserved to experience every second of it.
"You should go to him," Sam suggested, feeling out the flask at his pocket. It felt warm. "He's worried sick over you and I don't think making him wait any longer to see you would be fair." His hand found her shoulder again. "He misses you a lot, Ruby." Sam didn't think he needed to bring the other her up. That would just make going back complicated.