I buy a home with my son for him to live in. After 10 years, he buys my share for my original investment.Do I have a tax liability?

Its a bit hard to decipher your question based on the information you have provided.  I don't know what tax liaibility you would have - there would be no gift tax, unless the entire amount of your estate, and the gifts you've given exceed the federal combined estate and gift tax rate.  Right now that rate is over $10 million.  There might be capital gains tax to your son when he eventually sells the house, if he is not entitled to an exemption or if he exceeds the exemption amount.