Tina, how my heart aches for you and your loss. This month we honor my sister's passing 11 years ago. I have two brothers but, in all honesty (sibling wise) she's the one with whom I wanted to grow old.
And it takes you "as long as it takes" to finish a quilt. I have made several quilt tops but that's as far as I have gotten ... the quilting still needs to happen. You WILL finish it. Maybe for right now you could work on something smaller - a baby quilt or place mats are fairly quick to complete. I think you will feel better when you accomplish that. And as many others have said - there's no limit to the number of works in progress you can be creating at any given time.
Be kind to yourself and take good care.
Di