Is it, though? Really? Isn't it actually the most obvious conclusion? Other readings are possible, but all require a degree of wrenching. Why would anyone find it implausible that a man who wrote poems of love and sexual desire to both men and women (or to at least one of each) was romantically and sexually attracted to both men and women?
Occasionally I'm reminded that resistance to the idea of bisexuality still exists. I have to be reminded, because it seems such an absurd thing to be sceptical of that I have difficulty retaining the fact. Women and men are pretty similar in many ways, after all - much more like each other than either is like, say, shoes, yet apparently no one has any trouble believing in heterosexual shoe fetishists.
Perhaps it reflects a more fundamental preference for binary choices. I dare say I could come up with many examples, but here's one that's fresh in my mind. A few months ago I was in a research seminar on an article about George Herbert's The Temple. According to the article, the scholarly orthodoxy had been that the architectural structure of the book (which is divided into sections such as 'The Porch', 'The Altar', and so on) was purely metaphorical; but our author argued that, as a rural vicar, Herbert was very concerned with the literal fabric of his church, too. The answer to the question, 'Is the temple in The Temple metaphorical or literal?' turns out to be, 'A bit of both.'
It's convincing, but frankly I didn't need to be convinced. My immediate reaction was one of surprise that everybody didn't already take that for granted. Flattering as it would be to conclude that all this makes me a particularly subtle and clever thinker, I don't buy it, because these thoughts aren't subtle at all - on the contrary, they take (what seems to me) the path of least resistance through the texts. It's all a bit of mystery.