Before my pen has glean'd my teeming brain, (2)
This line isn't exactly about love in the traditional sense… but we sure get the feeling that the speaker has lots of warm and fuzzy feelings for himself and his own "teeming brain." At the very least, this quote evidences a healthy dose of self-satisfaction – if not outright self-love.
When I behold, upon the night's starr'd face,
Huge cloudy symbols of a high romance, (4-5)
Remember that moment in The Lion King where Simba and Mufasa stare up at the stars? It turns out that Disney was in good company… Keats seems to think that all his love (past, present, and future) is written up on the "night's starr'd face." Notice the personification of the night? If we didn't know better, we'd say he was planning to get it on with nature itself.
And when I feel, fair creature of an hour,
That I shall never look upon thee more, (9-10)
Sigh. Isn't love so sweet? Except, of course, when the speaker is already planning for the time when he won't have to hang out with you anymore. Notice how Keats turns the loved one into an object here? The "fair creature" is just a sight for his eyes, much like a painting or a statue. Is this an expression of true love? We're not so sure.