I am so sorry for your loss. Please do not feel bad (don't know if you do but you might) about not being there when your aunt passed away. The important thing is that you visited her when she was conscious and that she was part of your life. When my mom died a long time ago, I had a lot of insomnia from it (I didn't cry much). Everyone grieves differently. There is no "wrong" way to grieve but I agree with everyone that talking to a therapist could be helpful. You may have trouble expressing yourself in therapy at first, but, with time, you will become more comfortable. Therapy would help you with your social isolation. It could be scary at first but the feeling might diminish with time because you will slowly get used to it and start benefitting from it.
When I was suicidal, some of it was anger about other people's behavior or anger about life circumstances turned inward on myself. Think about it. Why should you die and your mother be the one that keeps on living? You deserve a chance to turn your life around. I am unfamiliar with what help is available in Spain (I am from the USA) but I suggest looking into what kind of support is available in your community. Time will help ease how badly your grief is making you feel. It is so good that at least you experienced kindness and love through your relationship with your aunt. Keep celebrating that. <<hugs>>