Grief resurfacing at big milestones

[d700]

I lost my Mother 7 years ago, when I was 21 and she was 55. 
I was heartbroken, but quickly took up a university degree 200 miles from home to help distract myself from my grief. Looking back now, I did not allow myself to grieve properly. 
I am now 28, and my life has moved to a point where I’m thinking about houses, marriage and children. 
Seeing my friends get married and have children and the precious memories they have made with their Mother’s has made me so sad for what I’m going to miss out on. I feel bad that my first emotion is sadness/jealously at such at happy time for them. Aside from big life events, I feel myself noticing my friend’s relationships with their Mother’s changing (going for meals and wine together, holidays together), that I have missed out on. 
Even thinking about my future life events without my Mother breaks my heart. I don’t know how I will get married without her there.  We were so close, and I know we would have been even closer as we got older. I am really struggling recently with these thoughts.