Pushing each other is good, within reason. In order to properly answer your question, you have to consider a few factors:
- How much time was spent exercising and how much time was spent talking?
- When you were done, did you feel like you could hardly move?
- Is your belly expanding despite all the work you are doing?
Training with a partner usually generates a lot of talk. This talk is good, particularly when you are discussing the merits of training styles, checking technique, etc. But it will extend training time a bit. If the 2.5 hours is a result of the talking, then you probably are OK.
The second point has to do with making sure that you don't push each other to the point of hurting yourselves. Motivate, but when form starts breaking down, intervene. If you are constantly pushing yourselves past the point of being able to train with proper technique, you are asking for injury.
The last point has to do with the hormone Cortisol. Cortisol is the stress hormone, and it is the body's natural reaction to any sort of stress--both physical and mental/emotional. Cortisol is a natural part of training. After you are done training, you will also have an increase in Testosterone. Cortisol is catabolic, with a focus on getting rid of muscle tissue that has been broken down, and converting it to energy. Testosterone is anabolic, with a focus on helping your muscles recover, triggering human growth hormone, which in turn builds muscle (assuming you are eating properly). The longer the training session the more Cortisol will be built up in your system compared to the Testosterone. The absolute amounts don't matter quite as much as the relationship. The common threshold for when the balance becomes more catabolic than anabolic is about 1-1.5 hours.
I wish I had studies to back up that figure, but even the articles I've found describe the phenomenon, but don't provide any sources for that information. The question is whether its the overall volume of training, or the time that is more important. And that I don't have an answer for. In general, if you belly is getting larger even though your eating is in good shape, that is an indicator of the type of effect Cortisol has on your system. Shortening your training time to about 1-1.5 hours should help curb that. If you still need 2.5 hours overall, you always have the option of splitting the training into morning and evening training to stay within the ideal time frames. If your belly is staying the same size, then I wouldn't worry too much about it.