You know it's just art right? I mean, sometimes people like art that depicts the opposite of in real life, especially when it comes to sex, but even other stuff. I play and enjoy grand theft auto every once in awhile but I would never enjoy the street life like that IRL.
Also, I'm not saying you're doing this, but make sure you don't confuse pics that depict consensual nonmonogomy with pics depicting actual cheating. I know there's a lot of both on here, but I think there's much less cheating.
Consider the following:
Searches for "(group sex || polyamory), -infidelity" bring up 12390 images
Searches for "infidelity" meanwhile bring up 4048 results.
And this only accounts for correctly tagged images. A lot of images are automatically tagged as infidelity by mistake when the artist actually hadn't meant to depict that at all. They are often in non-canon universes or timelines, etc. where one's canon lover might not exist or the canon couple never even met.
In reality, there's probably substantially less than 4,000 images of cheating on this site, and of those, the vast majority of people drawing or enjoying them are not advocates of hurting or cheating on their partners IRL. Those that are surely exist, but their numbers are definitely few and far between.
Also I'm not bashing you or making fun of you for being upset by it. Even I have to turn a bunch if custom filters on so I don't see a lot of art depicting terrible things on here after all the shit I've been through in my life, lest I go crazy. I'm just trying to cheer you up and give you some perspective. Have a nice day. :)