I guess you see what you have “lost” about her. But ask yourself if you ever really “have” another person?
The time, love and joy that people give is a gift and not a lifelong obligation. So what she gave you, you will always have. In time you will value that, without the regret and bitterness you feel now. I can’t assure you that all the regret will pass, but what little is left will be bearable and not get in your way.
It’s OK, healthy, to be sad and upset when there is cause, but not disproportionately. So try to distinguish between normal grieving activities, and the spiral-like thinking that characterises depression. Be busy and plan to be busy, to bypass the inactivity that allows negative-spiral thinking to emerge. Planning and doing what makes you happy, as often as practical, will make you happy. This is the essence of CBT.
And then you will find that happy people are attractive people.
Good luck