The best spells are those you write yourself. When writing, focus on the emotions inside and feel the energies flowing into the words. When doing the actual casting, imagine the energies flowing out of your heart chakra and into your throat chakra, imbuing the words with the energies.
I'd also like to give you some advice on this. You may think he is your soulmate, but he might not be. Instead of writing the spell along the lines of "make him love me", instead make it along the lines of, "if he is truly my soulmate, make him realise this and come back to me."