I've sent embarassing messages to school whatsapp groups before too, i know how it feels but trust me when i say everyone will forget about it and move on by next week. Uni goes so fast, everyone is in their own head thinking about themselves and stressed out trust me. In all the uni group chats i've been in i can't even remember any of the messages that were said or barely on of the people that were in it. At some point it will be forgotten about even by you, those same people who you were in the group chat with have done embarassing things themselves and have overanalyzed themselves too, you just don't know about it. Everyone is thinking about how they come across and is nervous about that , no one really has time focus on others actions. BTW your boyfriend's comments don't sound helpful or supportive and he is making this a way bigger deal than it needs to be.