Some facts about doing istikharah for marriage
The linguistic meaning of the Arabic word “استخاره” is to seek good, or خير.
It is not supposed to be some sort of magical ritual that will result in an immediate epiphany that will make clear to you the route you should take, or the decision that you should make, overnight.
Rather, when you pray two units of prayer at any time of the day (it doesn’t have to be at night) and then invoke Allah with the prescribed du’a of استخاره , you are actually asking Him to decree for you, between two options, the one that is better, for both your duniya and your Akhirah.
Whether you have received a proposal for marriage, or if you have someone of good character and lineage in mind as a prospective spouse for you, doing استخاره ensures that you seek that outcome/result from Allah that is better for you. استخاره is a du’a, plain and simple.
By doing it, you ask Allah to decide the matter for you Himself, by turning hearts and/or making events happen in such a way that things head forward either in favor of the union, or against it.
And that is precisely what happens after an استخاره: either a proposal becomes finalized and a marriage takes place, or such a marital union is averted, for one reason or another.