Breakup

My girlfriend of almost 3 years left me last June. We have been living together still since then. However, we need to move out of our house Oct 31 she has decided to move out in July as she said she doesn't want to work on us anymoreAfter months of being depressed and not really paying attention to herself in January she almost like flipped a switch. She stopped sleeping on our couch and in bed with me and started sleeping in our guest room. She searched high and low to find her sex toys and started taking better care of her body as in grooming. She claimed it was just because she wanted to start doing it. She later informed me that she was planning on moving in with her friend S. S. has spent the night at our house several times and slept in the guest room with my ex however she slept on the futon and my ex in the bed. She assured me that nothing was going on and that even though S. has feelings for my ex they were not reciprocated. My ex preached about honesty and even said that the reason we split is because I lied to her once. Now today I found out that my ex has been lying to me since January as I found out my ex and S. Slept in the same bed same room this weekend. My ex and S. have only known each other since january and are going to live together starting in July. I am struggling with kicking her and her son out or letting them stay until he finishes school. My ex tells me that we have a connection that shes never had before but that must not matter. Need advice pls