So far I've experienced suicidal thoughts for four years - nearly five - on and off. Every year without fail they return with two times the force they previously had but I have absolutely no idea why: I have incredibly supportive friends, a loving family and pretty much everything I could've asked for but the thoughts keep coming back.

I don't want help from here nor advice I just want to understand why. For further understanding they return on and off just by being a little sad (however the level of strength and if they even occur changes), during the summer (very powerful during this period and most common) and when I'm in a tough position in life (not surprising).

I find it extremely hard to talk about them (which I rarely do) without breaking down, even someone mentioning the idea of suicidal thoughts near me makes me a little emotional which I keep inside me but this doesn't happen over the internet as long as I'm sure no one I know will see it and know it's me. I'm 15 years old. I find it even harder to talk to my parents about the thoughts which I'm not even considering. 

My mood over the year: my mood over the year is during the entire year other than summer I find things easier, the thoughts rarely cross my mind and if they do it's relatively easy to stop thinking about them.  During the summer the thoughts (as I've said previously) are extremely powerful and appear with 2x the force they had the previous time I had them (including the spring, autumn and winter, stacking over time). 

During the summer period: during the summer it's very hard to not think about them unless I'm around friends/something to keep it off my mind but even that won't work for too long, my friends do notice that I'm not myself but I just don't have it in me to tell any of them. The summer intensifies the thoughts greatly and I often find myself during this time planning out my own suicide or writing suicide notes that I later scrap when I feel a little better. They often keep me awake overnight and during the summer I get little to no sleep doing frequent all nighters but for some reason a lot better or just normal the next day.

I just want to understand why.