[2:235] You would not be at fault regarding the proposal you present or hide in your hearts to women. God knows that you will be mindful of them; but do not make arrangements with them secretly, unless you speak honorable words.
What this permits includes seeking affection and laying the groundwork for the state of union. What it forbids is doing prohibited sinful acts or preparing for such an act.
[2:235 cont'd] And do not resolve on the knot of marriage until that which is written has reached its term; and know that God knows what is in your souls; so be fearful of Him; and know that God is Forgiving, Forbearing.
i.e., the waiting period of the first [marriage] is required so that respect for the deceased is not neglected.