I have the same problem. My bf seems to think I am perfect and do not need to lose any weight (I am 230lbs). I just have to keep reminding him that I am doing this for me.
We only get to see each other once a month which is hard. He wanted to plan a dinner cruise which I said no to. He kept trying to make reasons for us to go, how I could eat healthy etc. i had to be firm in my answer. We planned a comedy club instead.
It is hard, but just keep telling yourself, you are doing this for you. No one else. If he is slacking, remind him that you need support.