Trying to Grow

I lost my Dad when I was 13 to cancer; he was only 44. I have two brothers, one is a year older and one is eight years younger. We have all done our best to protect our mom and be there for her, making sure there were never weekends where she was all alone, etc. My older brother and I are finishing up college now and we have made sure our family has stayed close and connected with lots of phone calls and visits throughout these years. I think one negative that has resulted from us trying so hard to be there for our mom is that we didn't heal completely because we wanted to be strong.
I am so fortunate to have a boyfriend that adores me and my family. The past four years with him has only brought my family closer together; he is a real blessing and I believe he was a gift from my father. We are planning on getting married in about a year. I know this is another natural milestone in life, but I feel guilty as I grow older because I don't want my mom to think she is being left behind as my brothers and I move forward. She has never said or done anything to make us feel guilty or that we need to stay by her side, it is just what we have done and what has felt right. I know my mom is so happy for me and my boyfriend and all that the future holds; I just feel so bad because her selflessness has never failed. I don't think she would ever want to get married again, but thinking about her growing older and being alone breaks me.

Are there any parents out there who have a child that has gone through the same thing and would be willing to share?