Assuming there is no agreement about intellectual property rights the legal position depends on what rights are concerned. However, as a general principle you will own the rights in those parts you invented. If it is impossible to say who did which parts of the work, then the rights may be jointly owned and there are provisions in the various intellectual property statutes about this. You will need to negotiate a compromise. Perhaps each of you will license the other with rights you own and then go away and work independently or if one of you wishes to abandon the work then you may take a lump sum from the other as compensation.
Singletons are specialist intellectual property solicitors.
If you have a legal question which you would like answered then please write to the Editor, Inventors World, clearly marking your envelope 'Inventors Legal Problems'. We regret that, due to the complex nature of Intellectual Property Law, personal correspondence cannot be entered into.