All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
If this person is pleasing in his religion and moral conduct, then there is nothing wrong for you to supplicate Allaah to make him your husband. This is among the good things that are permissible for a Muslim to supplicate Allaah for; as Allaah says (what means): {And ask Allaah of His bounty. Indeed Allaah is ever, of all things, Knowing.} [Quran 4:32]
However, there is no use in always thinking about him and being preoccupied by him, as this is morally exhausting and time-wasting. Hence, you should try to think about what benefits you in your religion and worldly life until Allaah decides what is better for you. Nevertheless, you are not sinful for thinking about him provided that this does not lead to actions or words that cause the wrath of Allaah or to being determined to commit a sin, as you are not held accountable for your thoughts. Abu Hurayrah narrated that the Prophet said, "Allaah has forgiven my nation for their inner talk (to themselves) as long as they do not speak about it or act according to it.” [Al-Bukhari and Muslim]
Thinking about him may be due to your extreme desire that he becomes your husband. Nonetheless, we draw your attention to the fact that it is better to endeavor to repel these thoughts lest they would lead you to unpleasant consequences.
The matters that you mentioned are not necessarily related to the outcome of the Istikhaarah or its outcome in being enabled to do the matter on which you sought Istikhaarah or not, as has been clarified in fatwa 81434.
Our advice to you is to put the matter in the Hands of Allaah and supplicate Him as much as possible, and you may repeat the Istikhaarah.
In the end, if it is possible to marry him, then all the best; otherwise, you should not think about him anymore. You do not know where goodness is for you. There are many men out there, so ask Allaah to bless you with a righteous husband. Allaah says (what means): {But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allaah knows, while you know not.} [Quran 2:216]
For benefit on how to treat infatuation with a person, please refer to fatwa 84544.
Allaah knows best.