You are right, life is unfair. Some people have very tough lives, others have an undeserved breeze.
You sound tough, like a warrior. Yes, you have anger and resentment - understandably - but your difficult life didn't beat you down, it didn't defeat you.
Now, at 42, you are still young with so much in front of you. And you are likely so much more resilient than all those people who have never had a problem worse than a burst tire.
But, you gotta let go of that anger and resentment. Thats goal number 1. That is all that is left, to achieve your final victory over your difficult life. If you hold on to it, it will keep you as a slave to the past forever. Let it go, seize your victory.
Whats done is done and cant be changed. Agonising over it is only to waste your time. Let it go and move forward into a new and happier era. If talking about trauma is useful to you, then seek an appropriate forum for that, do not let it invade every aspect of your life.
You say you have no one in your life - that will come. You can make friends through activities, clubs, travel etc. You can go on dates via OLD. You can do anything you want, but first you need to let go this resentment. You will be much more attractive to friends and partners if you are positive and upbeat, rather than locked in a hopeless battle with an unchangeable past.
Stop fighting with the spectre of the past and start enjoying the present. It may seem difficult, but its just a state of mind. CHOOSE to be happy. Literally choose it, like you would choose a meal or a dress.
Yes, you cant be an 18 yr old going on holiday or trying new adventures, but you can be a 42 yr old going on holiday and trying new adventures.
A 42 yr old is just a 18 yr old with 24 yrs experience. You life experience is every bit as valid and precious as that of anyone else, dont forget that.
And you know, age is just a number! You can laugh as heartily, fall as deeply in love and enjoy a sunset at 42, every bit as much as can an 18 yr old. More even, given 18 yr olds are daft and dont appreciate anything!
Good luck to you. Take your victory, its right there.