You've taken the first step, which is admitting that you have a problem. That's good. Recognizing that your behavior is completely dickish and unacceptable puts you a step ahead of most other men like yourself.
That being said, I'm not really sure what to tell you. I didn't "fix" myself, I simply grew up. Jealousy and possessiveness are the result of immaturity, a lack of self-confidance, and extreme insecurity. You're always afraid that the one you love will leave you.
It's a self-fullfilling prophecy, dude. Keep acting this way and, yes, she WILL leave you. Any woman with a brain in her head will eventually figure out.... Y'know what, I gotta stop right there. I wish I could finish that lovely little fairy tale thought, but I can't. It's just not true. Truth is, you'll find a woman who'll put up with your bullshit. Why? Because people are stupid, and that includes women.
You'll only change when you grow a pair of balls and stop being a whiny little pussy about how everyone you love is going to leave you in the end. I could only fucking HOPE that would happen, cuz then it might shock you into changing. But it won't. Women are dumb cunts and you'll find plenty who'll stick right by you no matter how shitty you treat her.
Right now my first love, who I remained very good friends with for many years after we broke up, is sitting somewhere with her husband and son, probably feeling like an asshat. I haven't spoken to her in years. Her husband forbids it. The last time I talked to her, she was afraid of being on the phone with me because she feared he might have her phone bugged and would be angry that she was talking to me.
So, don't you worry yourself one little bit about being lonely. You'll find a nice sweet timid little thing who'll obey your every command. It'll never be enough for you, though. You'll never feel secure and your demands will get crazier and crazier over time. She may end up cheating on you. She may run away. Or she may just stand by her man, like the dumb fucking bitch she is.
My honest and serious advice is for you to go with your girlfriend to see a relationship counselor. Yeah, they're assholes, but you're a bigger one.
All my ever-burning rage,