Look up synonyms in a thesaurus to help you find the words that describe the way you feel about your man. There's nothing wrong with a little help from a dictionary or thesaurus. They are the tools of a writer's trade. Sometimes you may not be able to find just the right word, but you might know it when you see it. Using words that are not common can help make your poem more original and sound more sincere. Make a list of the words that accurately express your feelings for your significant other and use them to help develop your verses.
Structure your poem in the most natural way. Don't feel forced to rhyme words if it alters the message you want to send to your man. Not all poems have to rhyme. It's better not to rhyme than to use words to force a rhyme, especially if you don't feel comfortable with the words you choose.
Choose a moment the two of you shared. Rather than try and encompass the entire spectrum of feelings you have for your man, think of a special date or something he said to you that you remember and he will to. This helps personalize the poem.
Tell him how he makes you feel rather than how you feel about him. Your words can show him he's doing all the right things to make you love him the way he loves you.