I want to let her go before I become a crazy lady. But how?

I really need help. The story I am going to write would sound like I am a crazy and a horrible girl. But I at least I need to hear from you guys what I should do.

Ok I started working at this place almost two years ago and I met this girl there. At first I didn’t really know she is a lesbian until she came up to me and made a joke about her living situation with her girlfriend. After few weeks she started talking with me and after a month or so we became really good friends. Her charms,flirting, and very out going personality just attracted me a lot. We became such good friends and we started going out and mostly she would propose me to take her out so I would take her out for dinner. She never payed for anything but I didn't care about it. And this whole time she was with her girlfriend but this friend did not really care going out with me because she said it was really fun to hang out with me. She started talking to me over the phone for hours and hours about her relationship and how much she likes her girlfriend and her girlfriend doesn’t make any effort to keep it up with her and so forth. We used to talk with each other until 3am sometimes. It was mostly about her her and her. Also she got to know that I am coming from so to speak a "wealthy family". She told me that she is coming from a very poor family so it made me sad and I would buy her lunch and take her out to make her feel good.

Honestly before I met her I have never even met a lesbian in my life. I was a straight girl and did not even have a tiniest crush on a woman. But after meeting this friend I got REALLY REALLY close to her and she became REALLY REALLY close to me too. We would talk hours and hours (mostly I listen to her relationship problems) but I felt so good to have someone at least to talk because I have been so "lonely" for long time after my break up with my ex-boyfriend.
Anyhow, one time she came over to my place and she brought wine and it got me so drunk and she started seducing me and we started kissing and more after that. Next morning she woke up as if nothing happened and got out of my bed and went to see her girlfriend. I was so confused and shameful because she was still in a relationship and I did not think I like a woman like that. Well after the first incident we still kept on hooking up over and over behind her girlfriend. Evey time when she had a fight with her girlfriend she comes to me crying and find comfort in me. I started liking her a lot. I know you might be thinking that I am a horrible person to sleep with her because she was in a relationship. But neither one of us could stop it because as she said she was always done with her girlfriend but next morning she goes to see her. I was such a foolish person to let her in over and over trusting that she would build a life with me.

Time went on and I told her that I was starting to like her and then she got all offended and angry with me. She said I was only a friend to her and I do not know how it means to be a lesbian. Then she started treating me like trash. It made me look so desperate and I would do anything to PLEASE her because I liked her a lot. She started controlling me as if she was my girlfriend. At work I could not talk with other female co-workers because she told me i have to choose either them or her. (because none of the girls talk to her)I even gave upon my friends because she asked me not to talk to them. She became my one and only source of human connection because i was so afraid that she would leave me and I did not want it to be my fault all the time when she fights with me. I always was the fault and she blamed me calling so many bad words.
This year I lost my job and had to stop buying expensive things for her or paying the full price of a meal. I would still put more money than her. She hated it. She complained so much about it and gradually started stop seeing me often.
Now she started making me so jealous talking about new girls that she likes and how she makes out with them and about their intimacy and how great they are.

During a recent visit to her place, (she invited her new crush who met through social net work too) she treated me like trash in front of this new girl. Now I am so lost. I am so obsessed with her. I cannot stop thinking about this new girl and her (not to forget she is still with that same old girlfriend too). I feel so useless. I feel so lonely and spend time thinking about them. I even stalked few times. I cannot keep on doing this every time she likes a girl I get really sad, depressed and jealous. I have told her over and over that I like her but she has rejected me saying that she would not date someone who cannot pay for her stuff and pay her rent money .

Today she found out that I talked with one of my ex-coworkers (because she still work in the same company with her) so she got really mad at me and used very filthy language and said she is done with me because I betrayed her by talking with my ex-coworker. she never called me back again.
I am really sad the way how she just made such a quick decision and UN-friended me as if she is getting rid off trash.