I can't add much to what has already been written. As a parent I would have been very anxious had any of my children got themselves into a long-distance relationship, especially one with a significantly older person. I probably would have done my best to discourage such a relationship by trying to help create opportunities for that child to develop more local social relationships. Fifteen is a time when our friendships have a magnificent resonance, but when we also discover the world is far bigger than we thought. It is a time when hormones create emotional havoc in our lives and a time when sometimes we need protecting from ourselves. It is a time when there is no danger and everything is possible. Unfortunately people on the outside often see things differently. They often bring their life experiences to bear in seeing what's going on for others. I think your parents are probably very anxious for you and probably feel a lot less secure than the picture they present to you about how to help the son they love grow up healthy and happy.
To be honest, fifteen is also a difficult enough time with just getting through the day to day stuff too. School piles on the pressure and, awful as it may appear, should really be more of a priority ... easy for me to say
Depression is often a part of the emotional ups and downs of adolescence, but if you are truly dealing with suicidal thoughts you should really be taking steps to get some help. I would guess that it is difficult to discuss such intimate matters with mum and dad, but may you have one or two trusted and close friends? In England there are psychiatric support services for young people, but they are generally only accessible through a family doctor or a social worker or, heaven forbid, following a traumatic incident of some kind. Sometimes it is possible to speak to someone at school. I don't know what the system would be Eire, but in England (which in terms of school systems is often different from Scotland and Northern Ireland and sometimes even Wales) teachers have a duty of care to pupils in the place of parents while they are in school. I have a daughter who experienced mental health difficulties at around your age, including a suicide attempt. Please don't put your parents through such an ordeal. It is the worst thing they are ever likely to experience. She did get a lot of support from a young male teacher who gave up hours of his time listening to her, but his training did not prepare him for being a psychiatric counsellor.
If you don't find practical support from your established network of friends and contacts you might consider Childline who have an operation in Ireland.
This link takes you to their website. If you don't actually want to talk in person they do operate online chat session in the evenings between 6-10pm, but you have to register with the site first. Whatever, try not to let your depressions get the better of you. You are not invincible, but you can deal with your difficulties if you turn to face them.
Good luck, D. Keep writing if there is anything you think we might be able to help with.
Wishing you all the best.