Trainers frustrate me. Do you know how easy it is to get your professional trainer certificates? And many of them really don't know what they are doing. So many will tell woman not to lift weights (free weights) because it will make them bulky and all those other exercise myths that have been debunked a million times over. Finding a good one is very difficult.
You can do what you find works for you - and obviously you are making progress having lost over 10lbs already.
When you are ready, you can bump that up to 45 mins a day, and/or walking faster. But that also depends on your health and how your body can handle the workouts. (kneed, ankle, back pain, etc)
At some point I'm sure you will want to ramp up your exercise. And sometimes a little bit of tough love will be what it takes to make you motivated. I see alot of trainers going that "Jillian" route and its in order to make you mad enough to work out harder and prove them wrong. You do have to push youself and its too easy when you are trying to do it on your own to give in and not push as hard as you can.
Or, you could pull out the Richard Simmons workouts and get the gentle love that he gives.

Different workouts work for different people.
A good trainer is going to motivate you so that you want to do better. It sounds like although he may be a friend, he's not the right personality fit for you to be successful.