I guess there's many different possibilities here. Is it random videos with random partners once in a while or videos with an actual life partner? That would change the dynamic of the videos so much.
If it was, say, a solo model who once every few weeks or once a month has something new with a random guy, I'd probably be super curious to watch it.
If it was always putting out content with the same man, and if it was more than occasional, I might loose interest in those videos, but it wouldn't stop me from enjoying her solo stuff.
If it starts to replace too much of the solo content though, like if half of what she does is those instead of more solo stuff, unless i really dig the vibe between the two models, I might end up to stop watching her stuff altogether or very rarely.
The style of the videos would have a great impact too. I'm more into amateur stuff, so if it's full of edit and professional lighting, things like that, it's just not my thing.
A shaky, camera in hand, point of view video though, I love me some of those
As far as fantasy goes, I think it depends how you sell it. While I don't understand why, I know that many guys tend to get turned off and some even jealous at the idea of a model having a boyfriend or SO, so that's something to keep in mind. But I'm pretty sure you can still sell some fantasy like "oh i really needed dick so i grabbed a lucky guy on the street, maybe it could happen to you one day". I think POV videos can also help selling some fantasies.
Ultimately I'm pretty sure the actual answer regarding your own followers depends on your online persona, how you bring up those videos, and the relationship you have with your viewers.
For the price, it depends. If it was with a real life partner, I don't think I'd be willing to pay significantly more. But if it was with another model/content creator, i'd easily pay 1.5x, maybe up to 2x depending on the particular of the video, because of all the extra work/planning/testing involved.