Help and loneliness

Hi there never done this before but was wandering if anyone had any advice on how to deal with extreme loneliness and being stuck in self destruction mode to the point not coping daily and just see everything as catastrophic I am autistic and have adhd and other mental health problems and I am stuck in such a negative place and need help seeing the brighter side and on how make friends or meet people when can’t cope with the outside world or understand it I do have partner but struggle with that also since he very outgoing and also has cheated in past and now stuck in even more of negative thinking place where overthink everything to extreme more than usually do just over worry and panic about everything and wandered if this normal and if so how to snap out of it as on own and also have a son who also has autism and adhd and other disorders too  so is challenging when just us two and feel very isolated and wandered if anyone can help with trying to be more positive or to learn to cope on own fully without feeling extremely lonely or if anywhere can seek help to maybe find friends in same position 

any advice appreciated