Hi aabh and welcome. Really sorry for the pain you must be going through.
I think if you read around this forum as well as the Friends and Family of Alcoholics forum you will find many threads you can relate to.
https://www.soberrecovery.com/forums...ly-alcoholics/
There is a stickies section at the top of the forum there that also has many helpful threads:
https://www.soberrecovery.com/forums...c-reading.html (Classic Reading)
There is a book that is often recommended here, Codependent no more, by Melody Beattie. It's an easy read and has a lot of information in it about relationships and boundaries.
I'm sure you have asked yourself this. Why do you want to be in a relationship with someone who uses meth and cheats on you? You really deserve so much better than this true? Someone you can rely on, depend on, who tells you the truth and shows you respect.
I know it's hurtful when a relationship ends, but you can get through that and find happiness.