Oh Rufus, I'm so sorry you're feeling like this.
What comes across in your messages is how eloquent you are, and your self-awareness of your behaviours and beliefs that aren't serving you is incredible.
I'm sure you have already, but talking to your GP has to be a start, because you're right, this way of life must be exhausting and mentally draining - no wonder you feel so tearful and so drained. Don't sweep the suicidal thoughts under the carpet - they are very real and must be very scary and need to be addressed, so do mention those to your GP.
One thing you mentioned that really stood out was that you feel you don't have a purpose. Do you work? Can you work around your children? Do you have anything solely for you - a hobby, an interest, exercise, studying? I have a friend who, on paper, has everything you could imagine - no money worries, children, beautiful home, good health and yet she is the most unhappy, emotionally fragile person I know, and I think a lot of it comes down to a lack of purpose. Once the children are at school, she has nothing to occupy her time, her thoughts, capture her enthusiasm or energy, nothing ignites her passion or creativity and as a result, she feels utterly lost.
And I hear you completely about how you cut people off mentally even if you continue to interact with them if you feel they've hurt you. I do just the same and like you, I almost wait for them to hurt me, or leave me, which then makes it more likely that they will.
I wish I could off you more advice, but please see/speak to your GP and keep talking - I'm here, as are others, I'm sure.
Sending love and strength - you've been really brave being so honest about all of this, and you're not on your own.