Most Helpful Girl
You need to let this relationship go. Unfortunately this is a common issue among people who get together so young as you didn't get a chance to live your own lives, meet/date other people, etc. Not everyone will feel this way, but many will feel trapped and a need to explore. However, she should've chosen to do so while she was single, not drag you through her lying and cheating.
This has been a pattern that has continued for 8 years and is not getting better. You don't trust her, and you also don't feel safe with her. At any moment she will get up and leave. You need to see what a real relationship could be like with a woman you trust.