<human>: Last year around November my current girlfriend broke up with me for another man. I moved across the country for a new job. We talked and recognized we both made mistaken and owned up to them to each other.

 We got back together about 4 months ago and have been making vast improvements in where we went wrong the first time. We communicate on a whole new level, are more considerate of each other's feelings and the love has come back. 

I'm in town for the holidays and her sister, we'll call her (B), is home from college. This was our first contact since our split. I suggested to my girlfriend we have a Christmas at her house to include B. Everything went fine,  she thanked me me for the present I got her and we even joked with each other a bit. 

Then B made a comment about how I ditched her sister (my gf)  and it struck a nerve. For the past year I have been trying my hardest not to let comments  like these get a reaction out of me. Everyone in her family is under the assumption I broke up with her, which naturally evokes a bit of dislike for someone. Unfortunately, my gf for some reason can't or won't be honest with them about what actually occurred. I've been biting my tongue and now I'm tired of it.

Do I need to just tighten my belt tighter and stop whining or do I have a right to feel upset?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: gf dumped me last year,  she told her family I dumped her,  have been playing the bad guy for her sake.