<human>: My bf and I have been dating for a little over 8 months. He is sweet and very caring and has said multiple times he sees us being married some day. My bf has a past which we have discussed in length and he deeply regrets.

Two days ago I found out that he had a thing with my cousin. Two years ago they were talking as friends then they proceeded to actual date. The whole relationship ended messily. He thought it was mutual and there was no connection. He also placed their relationship length at 2 months. My cousin however was heart broken. She believed they had a future and that their relationship was actually 8 months. She even went through his extended family members to convince him to give them a try which was a big no-no for him. Obviously they were both at fault and a lot of it came down to communication.

My cousin is now happily married but this information hit me quite hard. Her sister [22 F] adamantly hates him and so does the rest of her family. A future with him would mean a strain on my relationship with them. Moreover, while they acknowledge that they both played a role in the break up, they still hate him with a burning passion despite knowing only one side of the story.

Do I continue with my relationship knowing he may be "the one"? Or do I end it to keep my relationship with my extended family intact?

Could you distill the essence of the text into 1-3 sentences?
<bot>: My cousin dated by bf and he broke her heart. While they are both at fault, her family despises him. Should I continue with the relationship even though it may put a strain on my extended family?