My boyfriend's family never accepted me as part of the family. You think?

I was excited when my sister visiting me the 1st time in 3 years. It was also my sister's first time to meet my boyfriend (boyfriend)'s sister. We all met at a Knott Berry Farm outing. When we were at the park, while talking, we learned that my sister and my boyfriend's sister's bdays were only 3 days apart. Amused, my sister said "hey, let's take a picture of me and my twin." She just passed me iphone and went over to her trying to take a picture together. But my boyfriend's sister avoided and refused. Boyfriend's sister was polite the whole time, but that gesture was distant and unfriendly, per my view. It was quite awkward for a moment. I pretended everything was alright during the outing. However, I still feel emotionally low after 2 days. Boyfriend is very closed to his sister and mom and he took time to propose to me. I always thought that had much to do with the influence from his sister and mom. I have known my boyfriend for 7 years. I struggled for a few years, then I put that thoughts of marriage aside and determined not to be married again (I was married once and had a child). Life had been peaceful since I put marriage aside. The incidence brought back the unhappy thoughts the whole family never accepted me as part of the family. Am I too sensitive or my feelings has merits?

Selected the category for mature answers.

If this is the first time that something like this has happened then I wouldn't worry too much about it because your boyfriend's sister may have been in a bad mood or something like that. However, if this sort of thing happens regularly, where your boyfriend's family is hostile and stand-offish towards you, then I would suggest you may need to speak to your boyfriend about the problem; you can't go on living with that sort of conflict in your life. Chances are that your boyfriend's family are a bit over protective over their son and need to realize that your not going to hurt him and your intentions are good.