I've had some tough times before with this, where her friends got involved.
Most Helpful Girl
Depends. A lot of my college friends didn't like my boyfriend. We were play fighting and he held my wrists a little too hard one time and bruised me (I bruise super easily) and ever since then they were obsessed with the idea that he liked to beat me :P They also generally just didn't like his personality. That made no difference to me - I knew that he'd never raised a hand to me like that or abused me in any way, we were genuinely playing around and we do that a lot still, and I liked his personality so I continued to date him.
I think that if my best friend (who is also his best friend outside of his brother) didn't like our relationship, then I would consider her opinion. She knows me very well and she wants what's best for me. She knows him very well and wants what's best for him. I believe her intentions are good and she is honest. If she didn't think we had a good relationship then that would matter to me because her opinion is very valuable. I may still consider dating him but I would definitely hesitate for a while and try to examine the situation properly.1
Most Helpful Guy
If any woman here says anything other than "If my friends don't like him it usually doesn't work out." They're a liar.2