In Edge of Tomorrow, when Cage asks Rita if she's tried having sex to get the time loop ability back, with whom does she mean, since they are the only 2 who have had the ability?
I don't think we should interpret Rita's response to mean she tried using sex to get the ability back after she had lost it.
Instead, I think Rita tried to transfer the ability from herself to the person she was in love with during her cycle at Verdun. (i.e. while she still had the ability.)
She watched that person die ~300 times, and tried everything she could think of to save them and/or share her "gift" with them. Hence her strong conviction that Cage would not be able to give it back to her again (through any means).
There's no reason to think the other person (sexual partner) had the Loop ability. That was never said or implied. She just tried things to heighten her awareness, like intercourse.
As far as we know know there were only two people with this gift / curse.
Sorry the answer is so short, but padding it out won't help anything.