In the Ars Amatorio, it mentions this, but just has oculos... spectare. Pretty boring.
To look deeply into something is inspicio, but this might be too clinical. Nevertheless, it could work.
However, maybe the best option is suggested by the following passage from the first Phillipic of Cicero:
Sed per deos immortalis!—te enim intuens, Dolabella, qui es mihi carissimus,...
(By the immortal gods!--when I look at you, Dolabella, as much as you are most dear to me...)
So, we see this word intueor which suits our purpose nicely:
Cum in oculos tuos alte intueor...
This has just the right romantic and intimate tone.