If I were in your situation, I would be very hurt. I hope your upcoming marriage will allow you to buikd for yourself the family connectedness that you don't get from your mom. Also, maybe your sister and you can take care of each other in a special way to ease the hurt that you both feel.

It's hard for me to read this as anything other than flat out rejection. Maybe it's time to give up on getting from your mom what she just doesn't seem willing to give.

It's understandable that you want to call out to your mother, "What about me . . . I am your child too." Hard as it may be. I would advize you to stop doing that. I would even consider not following your mother on facebook. Or, at least, not post angry comments. If someone ignores me, there comes a point where I am going to stop paying attention to them.

Life is long and your mom has many things ahead of her, one of which is growing older and someday losing her health. Someday she may regret not building bonds of love with your sister and you. Someday it may be your mom who is in need of feeling cared about. What goes around comes around. This step-sister of yours may someday not turn out to be the perfect daughter your mom might think she is right now.

The less your mom does for you, the less you owe her. Invest your time, attention and love in others who value you. Maybe it's time to give up on trying to get love and recognition from mom. Hard, I know. But letting go might bring you more peace.