The fact I'll die alone without ever feeling the love of a woman besides my mother and without a child saddens me. So, as kind of a consolation, I want to know... How does it feel? Being in love and being together, the sex part, just living together and all that...
I wouldn't class revenge fantasy as positive, if I'm honest.
Parts of your brain will fight you on this, but try and think of something "nice" that makes you feel a tiny bit better, or happier, or relaxed.
For me, it's stroking my cats and/or going for a walk, but it could be pretty much anything really - as long as it isn't "I just want to watch the world burn" type stuff.
This isn't easy, it won't happen over night, but if you keep trying to identify something like this, and then purposefully choose to do it on a regular basis, you'll have done the first 100metres.
Try to remember that part of your brain wants you to be sad and angry and depressed. You've listened to that bit a lot. But the bit that wants to be happier, that believes things can be better, is what is keeping you replying to this thread. Practise listening to that bit more.
I wish you the very best of luck. You can do this. You are worth it.