Hi and welcome. I've added a trigger warning because of some of what you discuss. It's nothing to worry about, it's just so others can avoid reading it if it will trigger them.

I think the first thing to say is depression does not discriminate, there doesn't have to be a reason for it. Sometimes it just is.

When you SH are you keeping it clean? Ideally, you need to go and speak to your gp. You could always see if there is a doctor who specialises in MH at your practise and request to see them. They can offer treatment, whether it is antidepressants or psychological therapies such as counselling or CBT. Have you ever had any bereavement counselling to help you deal with the death of your friend? That may be worth looking in to. And there are lots of helplines out there. They will listen if you need to talk when things get really dark.

Your fiancee won't understand if you're not honest with her. At some point you will to talk to her. If she doesn't understand then show her the Time to Talk website.

You've made a big step talking here. Well done we will support you as much as we can