because you aren't drawing effective boundaries.
your friends have shit all over your girlfriend to the point that youre coming online to deal with it.
at this point, you need to tell them that their comments are unacceptable or not tolerable.
if they continue, then leave the situation.
"Hey OP your girlfriend is an edgelord. did she cut herself today? har har dumb faggotry."
"Anon, I would appreciate it if you don't degrade my girlfriend in my presence. It's not cool bruh."
"blah blah keeps saying shit"
"you may find that funny, but I do not. Let's change the subject."
"blah blah your girlfriend is a bitch instagram ho other guy insults."
"OK, since you don't want to change the subject from the inefficiencies of my girlfriend, I'll be leaving now."
"Oh come on OP you're going to be a faggot pussy whipped bitch and leave?"
"I asked you multiple times not to degrade my girlfriend, and you are not able to respect my wishes so I am removing myself from the situation where you are free to spend all the time you like talking shit about her since you find it so terribly amusing."
then turn on your heel in a Niles Crane huff and leave.