~ it is normal when a serious or long-term relationship ends to be sad and maybe even grieve. That may be why you are crying; sad over the loss of the old relationship. Maybe you should give yourself some time to grieve the loss of your old relationship before jumping into another one, but that doesn't mean you can't be friends for a while until you heal.
If the sadness/crying lasts more than 3 months, then that would be considered 'clinical depression' and it would be a good idea to get some help. Do you have any family or close friends (like a girlfriend or loving sibling) that you can share your feelings with? Sometimes, talking helps and sometimes going out with friends and doing new things helps too.
A lack of sun can cause SAD (seasonal affective disorder; think that's what it is called) and you can buy special lamps that can help brighten up your home. Open the curtains and put in florescent bulbs; this helps too. Hope you are feeling better soon, hon; will be praying for you too.