i don't think there's an issue with shipping real people as long as the shippers keep the same boundaries as for fictional characters.
if you ship fictional characters that aren't canon, don't bother the actors playing them about it, they're not involved in the writing and have no power over it, you're just putting them in a bad spot.
so when it comes to real life shipping, just don't bother the people about it. go on blogs, forums, whatever, and talk about it there with others who are also into it, just don't directly talk to the people being shipped about it. and especially learn to separate reality from fiction. as someone that's been involved in fandoms for many years, i've witness plenty of times people having no respect for the partners of the people they're shipping and completely harassing and disrespecting girlfriends and wives all because they're in the way of the ship. if you wanna create scenarios where a guy in a relationship cheats on his gf/wife to fuck a dude go ahead and do so, but keep it to the fandom, don't go tweet at them or post it on their ig