The first means that you are planning to get married, that it is your intention.
The second I would have put as I'm intended to be married. Which is a pretty old-fashioned way of saying I am engaged (to be married). You do still ~ rarely ~ hear people referring to their fiancé(e) as my intended.
Hope this helps, Gary.
If you intend to get married, it is your decision. If you are intended to get married there is more the connotation that the decision is not yours, you are a passive party to the marriage. I'm intending to get married also makes the decision yours.