It is Ossur for any Male (Married/Unmarried) to LOOK at an ‘Osani Kirtzoinoi’ for whatever reason at all.
The ONLY exception is ones Wife, Mother, Daughter & Sister.
If one is dating a girl to see if she is suitable for him, he may glance at her to ensure there is nothing about her appearance that he dislikes in any way.
As it says in Kiddushin “it is forbidden for a Man to marry a Woman until he has seen her in case he sees something despicable in her and he will despise her, transgressing: “One must love ones friend like ones self”.
There is no Heter for a Guy to check out (excuse my language) every girl he comes across in the off chance that she may be the one…