Aziraphale had been long enough in Vallo to know people came and went all the time, and how just as surprisingly Crowley appeared, he could leave without a trace at any time. The only thing that mattered right now, was Crowley was here, and the angel would make the most of every moment.
Seeing how felt the same (though it didn't make much sense for Crowley to feel lonely - he would have to ask later), Aziraphale couldn't control himself any longer? And why would he need to, anyway?
Looking this way and that, he found the nearest flat surface to set his mug. Then, with free hands, he grabbed Crowley and held him tight.