Brother's wife-to-be doesn't like me and I've got no idea why

Dear Coleen I'd love some advice on how to deal with my brother's fiancee.

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They've been together for four years and for that whole time I've always felt like I've done something to offend her because she's so off with me.

She blows hot and cold - sometimes when we're with the family, she'll be sweet and interested in me - but other times she'll just ignore me and literally look right past me and won't give me the time of day.

My brother is obsessed with her, so I know confiding in him would be a waste of time.

They're getting married in spring, yet despite I being the only "eligible" woman in the family, she didn't ask to be a bridesmaid!