Castiel didn't really think that Meg was simply there for him because of the reasons they'd mentioned, although there was the fear that she was there for exactly those reasons. That she wasn't there for him because she wanted to be, because of her feelings for him, but simply due to obligation. If that were the case, he would released her of that burden and allowed her the freedom she deserved. She'd been held captive and tortured by Crowley for over a year. To put her in that role of care taker because she felt forced in that role, to him that would be no better than holding her captive. It was why this past week he'd tried to push himself, to try and adapt to being a human without the help of others, as best he could.
But then she told him that she loved him. And that changed everything. His eyes, they searched her features wildly, trying to tell if this was an outburst that she made because of the alcohol in her system or if she truly meant it. Hearing it, despite her use of profanity, it made that warmth in his heart take hold and he realized how much he wanted to hear that. It was late, of course, after he already told her this, but he would take it.
Her movement to leave, to flee, he was certain, it made him move forward himself and grab for her elbow, to turn her toward him. He wasn't forceful in his action, but still firm so he could somehow communicate to her how badly he wished she'd think twice about leaving. He wasn't sure how many times he'd seen her leave now and honestly, he hoped he could put a stop to it, despite how he was aware these feelings were something she wasn't used to and couldn't rightly sort through with ease.