Cross Road

So I'm at a point in my life where I am feeling so confused and so messed up. I love a wonderful man who has done so much for me, and I find myself thinking about the future and find myself scared. Is it wrong to look ahead and wonder what it'll be like based on what it's been like??
Can you love someone but not be with them? And if you love them but aren't with them is there any hope for a future together? How do you walk away from someone who you truley love without knowing that it's the right decision??? can it be undone or is it permanent? And if you aren't really happy will you ever be??
I have to admit, my heart is feeling pretty heavy these days. I have so much going through my mind and I feel so much that the two are coliding and I'm not able to make sense of any of it. All I know is that it's not fair to continue it.
Have any of you ever walked away from some one you love because of that simple reason that you do love them, but you're just not right for eachother. Or have you walked away only to realize later down the road that you do want them and you are right for eachother and it's to late to save it.
Or do we have to at times take a step back in order to save something that we want to save, that is worth saving?? Can you take a step back in order to move forward??
27 years old, (almost) and I've still got so much to learn in life. I could use all the help I can get.