Alright, this text has quite a few ringing alarmbells in it. I am sorry I did not see it earlier. Upfront: I wont sugarcoat this. Feel free to flame, hate or ignore me, but I feel you desperately need to hear this.
Lets have a look at the events in a little more condensed format:
- You returned from an extended trip to the states and found yourself alone, friendless and jobless.
- You hooked up with a teenage girl who essentially traded sexual favors for alcohol.
- You met her sister and immediately hit it off with her, falling in love and moving in with her.
- You spend about a year living together and things were fine, except for "minor" problems.
- An old friend of hers moved in, but you did not feel threatened.
- When she cheated on you, you did not confront her.
- When she continued cheating on you, you hoped it would drive her towards you.
- You eventually moved out and wallowed in self pity, missing the good times.
- You now distract yourself with casual sex without emotion with a fixed partner.
Now lets have a little deeper look at things, not the events, but what they did to you. The paragraph numbers refer to the list numbers above:
1. You were lonely and without perspective. Yet, instead of getting a perspective, finding a job, meeting people and getting your life in order, you decided to get drunk. This should be your first hint that you set yourself up for trouble. Substance abuse is never a solution or passtime. There is nothing wrong with having a drink as long as the drinking is not the reason to do it. Having a beer while out with friends is fine. Having a beer to have a beer is not.
2. In your lonelyness, you did not care for who keeps you company as long as someone does. Coupled with Nr. 1, you met up with people who like to drink to drink. The problem with that is that they don't care who keeps them company either, meaning they did and do not care about you. You effectively traded being lonely by yourself for being lonely together.
3. Falling in love is a beatiful thing and I would need more information to make a real attempt at an analasys here, but here are a few things to consider: When you met your ExGF, you were with her sister. Sisters talk, so its reasonable to assume she knew that you two had sex the night before and had met that very same day. In short, her first impression of you was that of a man who changes sexual partners like underwear and who does not bother with deep emotion before sex. Its also quite possible that from your ExGF's point of view, the two of you were cheating. How did your ExGF's sister react to this? Was she sad or mad at you? Jealous? Indifferent?
4. This is key to the entire thing. You said you had only minor problems, but does she agree? How did you guys spend your time? Did you get a job in the meanwhile or were you just drifting along? How much did you party and did you ever cheat on her? Did she think you were? How was your relationship with her sister, im sure she came around occasionally. Did you work on your relationship with your parents or make new friends?
5. This point really depends on the answers to Nr. 4, but the essence is that someone you did not know or trust moved into your house. You had suspicions that he was after your GF, but you resigned to the fact that you did not have a say in it. Did you actually talk about this or did she just make a decision and you consented with your silence? Did you try to get to know him and get a better picture of him, or did you stick with your first impression of a home wrecker and treated him accordingly? If there is one thing I learned about relationships the hard way, its that it is damn easy to drive your partner away from you if you keep only your own counsel and never reevaluate your intial assumptions.
6. When she cheated on you, you felt your suspicions about her friend confirmed, but you did not confront either of them. Your GF made a choice here, but so did you. In not confronting her, you gave her the impression that either she could have her cake and eat if too by keeping it secret, or that you did not mind. Given her first impression of you, both seem likely.
7. Here you are reaching at straws. Let me be frank, she invites someone into her home whom she shares a connection with. She sleeps with him and does not tell you about it and you are suffering quitely without a word. How the heck is that supposed to drive her towards you? Your silence gives her liscence to believe whatever she choses. She numbs herself with booze and parties while you sit at home. It is very possible that she tried to make you jealous to get your attention and your reaction is to take it and ask for seconds. Did you consider the possibility that she might have been devestated by your inaction and her friend picked up the slack, giving her the divertion she felt she needed? I am not trying to paint their actions in a good light, cheating is cheating, but people don't cheat simply to cheat. They have underlying reasons and desires that lead to cheating. Yet, you did not spend a single second figuring those reasons out and instead just accepted the facts presented to you.
8. This is were you give up. Instead of getting angry, making choices and drawing consequences, you simply walk the path of least resistance. None can help you here, except yourself. You yearn to solve the issues you two had, but you have made no attempt to. You say that staying with her would have destroyed you. In my opinion, you have already done a pretty good job of that yourself. She played a role, but not the main part.
9. And finally, this is were you delude yourself. You have replaced her with another person whom you feel nothing for. Instead of dealing with the problems, you create new ones in hope of forgetting the old.
With all due respect, you need help. You need to nut up and face the music and above all you need to be honest with yourself. No relationship ends because one person made all the mistakes. Its very easy to fool yourself into believing that if only your ex had done things differently, your life would be beautiful. However, you have made choices, you have taken actions (including inaction) and you have made mistakes that have lead up to your breakup. When you saw a storm brewing, you did not close the shutters or secure the door but instead sat comfortably in your living room and hoped for it to blow over on its own. Now it has and you sit among the debris of a destroyed house, blaming everyone but yourself.
When do you come to the point where you get angry and do something about it instead of taking shitshovel after shitshovel to your face? The fact that you posted here means you want things to change, so there is hope. But the only person who can make that happen is yourself. Once you realize that, we will be happy to help you with our advice, but first you need to figure out what direction you want to take and make the first step.