@TheFiller given that I'm someone that overthink things I can give you my speculations so don't think that they are sure things.
First of all her character... she is too much serious and is a pure virgin so, after said that, she'll never give her first time to a porn actor.
Second, in chapter 6 she said that for the movie they need an amateur couple and she said that if it will be with him than is okay... this imply that she like/love him and that can accept to do something like that only if he's the partner.
Third, the porn actress seems like both him and her so I don't think that will do something for hurt one or both of them.
Fourth, the bonus story imply that, for at least in the mind of the author, love with a AV actress is possible.
Fifth, the genre of this manga don't include drama (tag used for stories made for stimulate emotions in the reader) or drammatic (in this case it would be moments like he that struggle with his feelings if she become an AV actress)
Given this points, what I can speculate is:
- Last minute save with someone that appear that will prevent her debut, remember that in the "preview" of the next chapter the sentences uses the combo "?!" that is used for make appear a sentence both a question and an exclamation
- She and him have their first time under the eye of a camera and form a couple, from there there are various possiblity like they do other films or it was only one time.
- One or both of them at the least moment say that can't do that.
- It's all fake (I mean that there is for real a movie but they already found a couple for that) and that is a tactic that that actress is using for make a couple of the two of them... I consider this the most difficult thing that will happen but is still a possibility.