First things first, this might be a little hard to read, since english is not my mother language

I'm at my 1st year in university, and our class decided to create a whatsapp group to interact, get to know each other and talk about subjects that we all study
Sometimes, some off-topic comments are brought into the group, and I ussualy don't care about it, but this one got me right in the feelings
This guy sent an image that said "killing yourself is for weak people. Strong men marry and die slowly each day". The thing is, recently an aunt of mine commited it, and I am still very sensitive about it when it's brought by a stranger.
I calmly send a text that said "this group has 25 different people, with 25 different life stories. Please don't joke about something so serious as this" and went off for a couple minutes.
When I checked the group again they said that it was just a joke, and "you shouldn't be offended by everything" "watch out for this kind of things in your daily basis, you might get offended". I wasn't offended until this moment, I was just sad and send the text in case someone was going throught the same I am, but the fact that they said I was offended made me offended.
I said it's ok to joke about it in a group where you know everyone well, but not in one that you barely know someone, and then mentioned the fact that made me sad in the first place. He responded with "well you didn't said that in class" as the fault was mine.
I thought it was completely disrespectful of him to say this, so I returned to the 'joke' and responded "well, if you think is that hard to be with a woman, go find yourself a man" which is disrespectful if you consider the "conservative person" fact
Until this point I totally thought I was absolutelly right, but then this 3d person entered the conversation and said: "we shouldn't post everything in this group and we also shouldn't polemize everything. Let's keep it cool."
When I read it, I immediately thought if I overreacted about it, that I should've not continued after the 1st text or even just ignored the message and pretended it never happend

So AITA?

Tl;dr: someone send a killing yourself-sexist joke and I said it was unaproprit. It escalated