This is short so I'll skip formalities and TLDRs

Something I learnt along my RP journey.

Dread works best when it is implicit, when it is conveyed in the subtext, when she gets her hamster spinning. "Is he seeing other girls? (hamster spinning) " vs "that asshole is seeing another girl" (she already knows, so no hamster, so no dread).

Are you dressing up a little too well all of a sudden? Have you started shaving more often? Have you changed your perfume recently? Are you getting more in shape? Why???? (hamster on overdrive)

She'll try harder for you when she senses competition. But she may just give up when she knows for sure that there is some else.

"This new girl in the office. She's really cute. I was chatting her up today" - you gave away the magic. You didn't give her the chance to wonder. Yeah, you can tell this to your male buddies and they'll say "nice". But for her there may be some jealousy but more of "whatever!".

"This new girl in the office, Sharon, she's really funny. She cheers up the place." - Nothing explicit here. Just something that happens in your office. But this stuff is gonna spin some stuff in her head. "Is she pretty? Does he talk to her a lot?" Don't give away the magic. If she tests you, make it seem its cute for her to worry or AA.

Never ever explicitly state that you got this thing for this other girl or some other shit to invoke dread. Use actions, not words, to convey dread.