Hi,
I’m sorry to hear about the loss of your mother and that you are suffering right now. Your post is titled by a reference to your breakup ‘four years ago’. There is nothing odd or unhealthy in missing someone from your past. I personally don’t think that four years ago is a particularly long time, especially since you were together several years. It sounds as if this ex stands out from the others and this can cause you to think there is something particularly significant about her, which may be interpreted as an indicator that you are supposed to be together. This may be true and, if it is, the only practical advice that can be given is to get back in contact with her. I know this isn’t easy and if she is still in a relationship then getting back into contact for that reason isn’t really advisable. This then leaves acceptance. I know you feel depressed and that her absence is a void, but there is a chance you are projecting your salvation onto her when really you need to working on accepting being single and being happy with being single. Fulfilling, successful relationships are amazing and the healthiest/happiest ones are the ones where each individual is content with themselves. Otherwise the relationship is just an addictive clinging, which leaves each individual feeling constantly anxious in case the relationship comes to an end.

Real strength and contentment will come from putting yourself first and this means you alone, not an idealised relationship. No matter how great she is, she can’t ever save you because you can only do that for yourself. Even if she showed up at your door right now and said ‘I love you and want to get back together with you’, soon enough cracks would start to show because your depressed/suicidal thoughts will not simply be dissolved by being with this girl, even though that is what you think you desperately want. Aim to get some help for your depression if you haven’t and look into its roots; try to detach its roots from her. Most of us are in the habit of looking back on the past through rose-tinted spectacles. Can you be sure this isn’t happening now?

Good luck 🙂