For love, all love of other sights controls,And makes one little room an everywhere (10-11)
"Sights" here could be as broad as "any object I see," or it could refer more specifically to "cool stuff in foreign lands like Machu Picchu." The point is that true love is kind of like a black hole, in the most romantic way: it sucks every other kind of love inside it. No matter how many Delta skymiles you've accrued, once you're in bed with your beloved, you'll never want to go travelin' again.
Let sea-discoverers to new worlds have gone (12)
In 1633, the year this "Good Morrow" hit the world in published form, the Age of Discovery was still a happening thing. Dudes with telescopes were hitting the high seas, eager to catch a glimpse of mermaids, monsters, and new continents rich in silver and gold. The known world was still expanding.
Let maps to other, worlds on worlds have shown (13)
New lands need new maps. But these maps were so stuffed with fabulous new places that it often looked like each place contained countless other, smaller places. The whole world was full of other worlds! Of course, the guys in the poem couldn't care less. Let others pay attention to that stuff. We've got some lovin' to do.