Confused and looking for advice

[jmw1075]

Several months ago I was contacted by a girl that was 13 years younger than me over Myspace, she was 21 and I was 33. We exchanged phone numbers and began talking. She seemed really nice and down to earth after talking awhile we decided to get together sometime. We ended up getting together the next night and I quickly found out she was a party girl and was out drinking almost every night. We had sex the first time we got together. She also did not disclose to me initially that she was actually still in a relationship when ours began, however she ended that relationship within a few days. For a few weeks we continued seeing each other and having sex frequently and during this time I foolishly began paying bills for her and buying her things. Then one day it was like she lost all intrest in getting together with me or having sex with me but she still continued to call me every day acted like everything was ok. I quickly learned through mutual friends that she was spending alot of time with another guy her age. I asked her about it and she denied that they were anything more than friends.
  I took her word for it even though other people told me there were having sex and that they were out drinking together every night. This went on for a month or so and I continued to occasionally give her money and pay bills for her hoping to salvage what we had at first and she would always till me she just needed time to herself but led me to believe she was still interested in me. During this time I developed very jealous feelings about the situation to say the least.
 Then one day she informed me via e-mail that she was going back to the guy she had been with before me and she changed her phone number and I didn't hear from her for a few months. I was told by mutual friends that she also stopped talking to the guy after me as well. I was hurt for a awhile but eventually got over it.
 Then one night about 3 months later, she called me and told me that she was single again and told me she wanted to get back together sometime and hang out and she also apologized for the way she treated me. Like a fool I gave into her, which led to me paying some bills for her again despite the fact that we never really did get back together at all and everytime I would ask her about it she had an excuse not to see me.
 Eventually though I met a wonderful girl that I am now with and I kinda lost intrest in this girl. However she called me a few days after meeting my girlfriend and I told her that I had met somebody. She said she was happy for me initially however over the next few weeks she began coming onto me very strong. Doing things such as giving me outright invites for sex, which I always turned down. I know one mistake that I have probably made is hoping that maybe I can somehow salvage a friendship with her.
 Recently she began confiding in me and telling about all her lifes problems and she inadvertanley told me that she had been sleeping with this other guy and was upset that he had treated her very bad and was into drugs. I did the math and figured out that she would have been sleeping with this guy around the time she began calling me after I hadnt heard from her in a few months, when I had began paying bills and stuff again.
 Even though I am very happy in my current relationship I felt so jealous and direspected when I heard this that I had a hard time even eating or sleeping. I feel so ashamed because I don't feel I should have these feelings about a past relationship when I now have a good one. Does anybody have any helpful advice for me to better cope with this?