I believe, like everyone else, they got together s3-4. Greg obviously knew he liked Nick early on, like pre-pilot, and tried so hard to impress him in a straight guy kind of way, because he got that vibe from Nick but he wasn't exactly 'out n proud', where as Greg is/was pretty ambiguous. You can see Nick warm up to Greg in season 2, being closer, more comfortable, and more teasing in a elementary school crush kind of way. Once s4 hits you see a shift in them, Greg is still oh flirty Greg but between the two you see they're more comfortable around each other, their flirting is more subtle, and if ever they do talk about girls or something like that it's always in a :winkwink: type of way. And, yes, they are together now, serious and connected and very professional at work aside from cute little looks and their 'talk like this incase someone hears us' kind of banter. September can not come fast enough.