So my boyfriend wants me to meet his family this Christmas and I'm really nervous to go because I dated his brother for 6 months and I never told him (my boyfriend) about it. I just never thought I'd get serious with him so I just never told him and things just got more and more serious and I feared more and more I'd lose him if I did.
During your relationship with your "official boyfriend"? Common sense says during 6 months, you don't just meet up for milk and cookies all the time.
Provided you cheated on him, this farce would be over. If you dated his brother for 6 months Before you got together with your current boyfriend, then that's not an issue.
It's really fascinating how you say "I worry I'll lose him if I told him". I try to maintain a neutral standpoint, but I just have little to no respect for people who prefer to live a lie. Why? Because it always catches up with them. Always