I could really use advice!

Okay, so I'll try to sum this all up short. Just some backstory: My boyfriend of 3 1/2 years and I are planning to attend his cousins wedding in late January and we need so much for the plane ticket and so on. Well he just recently finished the semester and started winter break. He went back home, which is roughly four hours away from where I live. His plan was to work and save up money for the trip. I took up more shifts at my job as well, so that we won't have any finacial problems when we go on the trip. This is where things start to go wrong. He's back home and has been there for roughly a week. The whole reason he went there was to WORK, and so far all he has done is go out every night and drink with his friends. So he hasn't started working and the money that he has and the money his parents give him is going to alcohol. I honestly don't know what to do. And what's really been the cherry on top, is that right now as I'm writing this, he is out for coffee at IHOP with a girl that I really don't like. On Facebook, she posts trashy looking pictures of her dressed up at Comic Con. I've met her once and she has a very piss poor attitude. But my boyfriend has known her for years so he considers her a good friend. While I know he wouldn't cheat on me, especially with HER, it doesn't stop me from feeling betrayed by all the partying and staying out late, when he told me he would be working. Meanwhile I'm here working my butt off, wasting my winter break so that this trip will be relaxing. Any advice would really be appreciated. I love him so much, but honestly I don't know what to do.

Edit: We had a talk. And things went kind of neutral. I told him how I feel able him going out with the girl for coffee and he chalked it up to me being insecure in the relationship. Typical guy response. I had a talk with my mom about everything and she had some good advice. "You can't control what someone does, you can only control how you react to it." For the comments about me paying for his half of the trip, I flat out refuse to cover for him if he doesn't make enough. If he doesn't want to try hard enough, I'm not letting him fall back on me. He's 21 and I'm 18.

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