It's pretty obvious that our speaker is in love. But since he spends all his time talking about this love (and in particular, the woman he loves), we don't hear much about the man himself. Still, through his words we're able to get a sense of what kind of guy we're dealing with.
We're pretty sure this is an adult – maybe even an old man – because his love is incredibly mature. He doesn't love this woman because of the way she looks, but because of what's on the inside. His maturity also shines through when he conveys that this woman's love for him is just as important as his love for her ("thanks to your love" ). It's not all about him, it's about the relationship.
Don't worry, "Love Sonnet 17" is not all about boring adult love. The speaker is also a pretty passionate guy. He likes to have secrets (that makes love a little steamier, probably) and he imagines his love growing inside him in a truly physical sense. This is a man who has thought a lot about love, both emotionally and physically.
One last thought: could it be that the speaker of this poem represents both sides of a relationship? Because there is no distinguishing the individual (they are one, remember?) either person in the relationship could be speaking this poem. Gives it another layer, right?