My ex is an actress. It never bothered me really. She saw it as part of the job and I do too. I'm the one she's looking for in the audience and taking her home at the end of the show lol.
I'd be curious to see the data of married Hollywood celebrities and how long their relationships last vs how many intimate scenes they have on film are. Of course, the data would be nearly worthless because humans are complex and there are millions of valid reasons why a relationship would end, but I'd like to see the numbers, anyway.
My wife went to school with someone from a popular TV show a few years back, where she'd be in sex scenes fairly frequently (from what I hear, I watched a few episodes and hated it). She had a long-term boyfriend at the time, and it didn't take long for him to not be cool with it.
She also went to school with a musician that had a stab at a solo career. She had some raunchy scenes in a music vid, and that quickly led to her breaking up with her boyfriend.
Those are my only two frames of reference, but I imagine it's quite hard to deal with emotionally, even if you know it meant nothing and is just a part of the job.
Let's be real. A lot of people in the comments are saying "it's just a job", but that's irrelevant. Prostitution and stripping are both jobs, and I guarantee those who work in either have a vastly more difficult time finding people okay with that.
Is it impossible for the significant other to be okay with it? No. Will it be harder to have a relationship? Definitely.
It really depends on the actor. I think we can all agree that not every actor has the same emotional maturity and therefore will not all react the same to it. For example, take a look at what Jonah Hill expects from his partners versus Ryan Reynolds and Blake Lively seeming to be a healthy couple while both have had some raunchy scenes in movies featuring other people.