My boyfriend and I live with my mom who has no respect for herself or us?

My mom was having an affair with a man and he basically screwed her life. It isn't all his fault, she let her business go under because she didn't spend anytime there but she doesn't see that it is their fault. She moved in with us under the pretense that we would her help her get back on her feet. That was two years ago. For the first year and a half she told us that she wasn't seeing him and there were multiple times when it transpired that she was and he had been round to our house without us knowing. We have been close to kicking her out before but she always plays the victim and at one point threatened suicide. We moved to a slightly bigger place so that she could have more room and she started paying us more rent as she now has a stable job. I recently found out that she has been talking to the guy that she had an affair with and he was meant tocome round our house. It also appears that there have also been multiple men off of dating sites that have been round. I know this because I went through her ipad as i knew there was something going on with her. She has stopped talking to my sister about anything and has stopped going to her therapist. I know I need to do something but I'm not sure how approach her. If she is ever confronted she just walks away and doesn't ever discuss it. Me and boyfriend are at the end of our tether. We want to have our own life but I don't want to lose my mom.