An original and successful work (usually not film, because that's where executives have a field day) survived all on its own without a romance subplot .
However, studios think that every story needs romance.
Alternatively, Bob is an Overprotective Dad, Alice is his daughter, and Charlie is her boyfriend. When all three parties are devoted to each other in some manner.
This needn't be sexual, but this is the type that's the most compatible with polyamory in its various forms.
We texted constantly for about five days but then he suddenly stopped.
I left him alone because I didn’t want to come across as annoying or something.
It can involve as many people as you like, turning it into a square, pentagon or more, but ultimately the love remains unrequited. Alice wants Bob, who is already in a relationship with Claire. Alice might try persuading Bob to give up on Claire.
Bob is unaware/neutral (leaving Alice as a Hopeless Suitor), or is aware of the interest and can't/won't reciprocate (leaving Alice in the "friend zone"). If Alice is Axe-Crazy (or otherwise extremely jealous), she might attempt to Murder the Hypotenuse.
Or Bob is in a relationship with both Alice and Charlie, while the latter two are friends but not intimate, possibly due to Incompatible Orientation. Bob and Charlie are best buds, brothers, or (rarely) lovers, but both are getting it on with Alice.
She could be playing both of them, but if Charlie is knowingly in on the affair, it could destroy his relationship with Bob should the latter find out. Bob and Charlie are attracted/loyal to each other but are also attracted/loyal to Alice. Alice is in a relationship with Bob and Charlie, but Bob becomes attracted/loyal to Charlie.
There is a lot of good drama/comedy in that little conundrum.
Even if the writer chooses to challenge that assumption.
Bob and Charlie might be best friends or siblings, and much of the conflict comes from wanting to pursue Alice but not wanting to hurt the other. Bob and Charlie may or may not know about the other's involvement with Alice.