It's been said--somewhere on this forum I believe--that 80% of weight loss is diet. Exercise is great; it will help you get in shape, healthier, and toned, but in the end, if you want to lose weight, you are going to have to change your diet. I have an associate who runs marathons and he was just commenting to me the other day about how he sees lots of people in these marathons that are clearly in better cardiovascular shape than he is--they can run farther and faster--but they are overweight, sometimes surprisingly overweight.
At particularly high weights, sometimes exercise alone is enough. But you are now less than 40 lbs from your goal (which is fantastic--you've made a lot of progress ). At that weight, I think it is going to take a concentrated focus on your diet to get to your goal and it sounds like you've been a little half-hearted about it up until now. I think 1500 calories a day is a great starting point, with tracking and measuring of everything you eat.
Also 10 lbs or one pants size in two months might be a little aggressive. That's definitely a "stretch" goal. It might be doable, but I don't think it will be easy. I think you might want to go back to your boyfriend and renegotiate the arrangement. Maybe he could pay the amount he was paying for the cheaper gym and you could make up the difference, with no conditions on his portion of the payment. I also think it might be worth trying to negotiate with the gym. You would be surprised what you can negotiate for. Tell them you can't afford the membership rate and that the other gym is $$ cheaper but that you'd really like to stay with them, can they do anything for you.