We could summarize this poem really quickly by saying it's about a guy who's in love, like really in love. Of course, if you described it that way, you wouldn't really get the gist of just how bad the speaker has it for his lover. It's bad, y'all—real bad.
He starts off by telling us that he's off on some fabulous journey deep into his lover's mysterious eyes. We hear all about how she has amazing powers over him. This lady can open and close him emotionally with the flick of her hand or the smallest of glances. The thing is he seems to be just as happy being shut down as being opened up. Whatever she does is amazing to him.
The speaker takes it even farther when he compares himself to a rose being opened and closed by the seasons. He even goes so far as to say that his lover can open him wide to the infinite: the universe, death, and whatever comes after. In the end, he admits that he has no idea what gives her so much power over him. But whatever it is, he's more than okay with it. He's obsessed.