"but I had been stealing backpack that you had lent me" What is this,makes no sense,sorry. Cannot correct it if I dont know what your trying to say.

I went for a walk with my friends, and we stopped to take some photos. I would add an "and". The last part is not clear. If she lent you the backpack, then you did not steal it. I think you need to think again about the words "lend" and "steal". Also, the last part seems very different from the first two parts, so I would put it in a different sentence.

Ha ha Hello where are you meet

The last part of the sentence is incorrect, and I'm not sure what do you want to say here so I could think something that you want to say, maybe: but I had been stealing "the" backpack that you had lent me. Here, you did not add the definite article in front of backpack.