You are not alone. My relationship with my ex ended three years ago. I moved out when I found out he's been having an affair. Lied to me repeatedly. I miss my old life terribly at times but my new life is not so bad.
Think small at the moment. My brother was very helpful to me during this time. I was talking to him about work and the fact that I used to go across to Asda every day at lunchtime and buy the same sandwich. He said to me buy a different sandwich. If you put your shoes on in the same order do it in a different order. Change your routine bit by bit so it's not the same as it was before. It helps solidify your new way of thinking so change becomes easier to accept. He's been in AA for years so his way of thinking is interesting.
Another big source of support for me was a Facebook group called Runaway husbands. I don't post that often but when I have the support has been amazing.
Don't even think or consider about a new relationship. That is the least of your worries. I have done some online dating and it's rough out there. I do have someone in my life but I don't see him much as time is short. I like him and his company but I couldn't live with him. I work four days a week and still have kids at home. I'm 53 by the way.
Therapy is very helpful. You need to be able to see yourself as others see you. Because you're going to be very down on yourself at the moment. Be fair to yourself. You're surviving one of the worst experiences I've ever dealt with and I've had a lot of grief in my life. What would you say to someone else who was in your position? It would be damn look at her surviving and living and being just fine on your own. I know it doesn't feel like it.
Have you thought about having a weekend away? I went to my brothers in Devon for a week soon after and it was so helpful.
Feeling lonely is very normal. Feeling like you have no friends is normal. You're not pathetic. You're doing really well and writing a post on here for advice from strangers takes courage. Continue to find support wherever you can and life will start to look better.
Oh and screw your MIL. I spent so much time with mine and gave her a lot of support and she couldn't give a shiny shit about me. She's not worth your headspace.