I'm sorry :( I know it's tough but hang in there. Time won't take away how you feel necessarily but it will help you gain some perspective
First I want to say that a lot of times when some one causes us to feel abandoned we need to look inside, and reflect to our childhood to see where during our childhood and sometimes adolescence did some one "abandon" us? It may be that this overbearing feeling of being left is due to preprogramming you have from your earlier life. If so, then one of the best ways YOU can rescue yourself from this is by seeking counseling. Over time working with a therapist will help you to see things differently which will then help you feel less bad about being left :) You CAN transcend this!
Second, a lot of times peoples decision to leave or stay with us is most of the time about them not us. You see everything is a choice ..aka "free will" so another way that you can help yourself is by accepting that even though it may make you sad to see some one go ...its their choice much like you choose who you stay or go with.

Those are a couple of ways that I personally have found success with dealing with "being left".
In the mean time, now is the best time to reach out to your support group. That could be close friends and family. That's going to help you get through this. Who knows, maybe you'll even discover, you're not the only who feels this way or who is going through this ;)

I also wanna add that everyone feels some kind of pain when theyre left. The only difference between all the people that have felt the pain you're dealing with now, is how they deal with it. You wanna gain control of your mind first. The way you see the situation will ultimately decide how you feel. If you feel " Why me! I can take this!" verses " I'm so sad this person chose to leave but I'm gonna get through this difficult time in due time" Hope that helps :)

Thank you so much for responding. I do believe there is much validity to what you are saying. I do think I have inadequacy and abandonment issues that stem from my childhood. I truly appreciate your insight and your taking the time to write back to me.

You're so welcome and I'm glad my insight helped! Hang in there!

Be happy, better sooner than later. It can be, and is, emotionally devastating when someone leaves after 20 years. If a girl leaves in a year or so, before marriage, be grateful. She saved you some real hurt.

Better when you are twenty something, then forty something. Find another girl and move on. She did you a FAVOR.

Smile and be grateful.

No one ever said that relationships are so hard sometimes and that no matter what you do it’s impossiblw to make someone be how you want them to be
I’m going through so many issues with my husband and many times feel like he’s just making me the bad guy when all I have done is try

I am feeling very similar things right now. They aren't fun. It is really hard, but I am trying to remember that I have gotten through tough spots before. Just wish I could be on the other end of this one already. Remembering I have gotten better in the past is helping.

Thank you so much to everyone who has taken the time to respond. Knowing that there are others out there and that people care enough to write back is making a huge difference. Thank you all so so much.