How do I tell the girl I date that I may be dating other girls

In last year I went through serious betaization process and I was beta even before. I met girl on dating site and I fell in love with her when we first met.

She was the most narcistic, selfish, manipulative, false, lying person I've ever met. Yet, even all the shit she's done to me, I continued to chase her. When we were together, she just used me, in the name of the family life, proper partner should take care of his dear (by buying shoes, clothes, paying trips, paying everything). She is also sociopath, fears facing other people. In the beginning of our pseudo-relationship, she found every flaw in me that wasn't consistent with her view of ideal "family type" partner. Instead of valuing myself and saying "well, it's me, you have to accept it", I was changing views, chaning my lifestyle, just to appeal her. True beta. According to her, I should have no friends or activities not involving my girlfriend, we should just have each other and nobody else, friends are just lying cockroaches who want to use me.

Example: After we first met, I was going home in train and some drunk guy annoyed young girl on seats beside me. I was full of fresh ideas from her (you don't care about other people). All I had in my mind was how lucky I am! But old part me was kinda uneasy seeing that young girl getting harassed (yeah, in the end he touched her on legs). I had the perfect plan. I'll pretend I'm her friend and lure her out. She was dumb, she could just politely apologize and change seat. But in the end I didn't do anything, and I was happy wit myself. I mailed to my new love and she replied that she had several similar experiences. After that, I realized what kind of asshole I am, and wrote her, that on second thought, I should have helped that girl. She got pissed, that she writes me about herself and I immediately start thinking about other women. I tried to explain her my intentions for week or more but it eventually died out.

She wasted my time, so many times. I belived her, everything, that she seeks faithful introvert mate. I started to suspect something in the beginning. Long story short, since the beginning, I wasn't the only one. I was being led all the time. I don't want this to ever happen to me again.

Do you need anyone for this thread, or..?