A friend of mine has a business idea. He asked if I knew how to make (smartphone) apps, and I said yes. I recently graduated and currently have some spare time for a side project and could see this being valuable experience to present in an interview, even if the business doesn't prove to be profitable.
I met with my friend a few times to discuss the business and the app he wants for it, and at first things seemed reasonable, though now he wants me to help with side projects and the actual running of the business. I told him I said I could help make an app, not be his e.g. account etc. He just argues "we need to start small" and "it's nothing complex". He has also been messaging me and acting like he's my boss and has gradually been increasing the work load.
I find him enjoyable to hangout with, we both have the same taste of music and enjoy going to venues together. But I really don't appreciate how he's acting as if I agreed to do all this work and isn't listening to my concerns. It's really getting annoying, he's texting me "are you at work?" and when I reply "yes" he replies "does everything I sent you make sense?"
I've been ignoring his texts and call or telling him I'm busy but he doesn't seem to want to take no for an answer. How can I tell him I'm not going to build his business for him and still remain friends? How can I avoid arguing with him?
We live in North America and my friend is Filipino. I noticed some people are very good at wording things and making the situation very difficult for their request to be decline, and I've noticed Filipino can be like this.
If this were professional work there would a long legal contract specifying the exact nature. Normally with friends, is it really necessary to state before starting "I have the right to stop helping you at my sole discretion and may become busy with other work"?
Edit for answers given: I know if I ask to get paid he would just say "when this takes off you will get lots of money". Of course there's no guarantee of it taking off.