Akbar,
Without knowing your circumstances, nobody can offer legal advice. However, regardless of who is currently paying the mortgage, you jointly own the property, and who has paid what will be considered in any final settlement. You must seek legal advice now.
It will help if you have a Declaration of Trust between you on the property, which should set out what happens if you split, but from experience, if someone is occupying the property and excluding you (which they are not permitted to do without an order), the law (Trusts of Land and Appointment of Trustees Act 1996) is very vague, and seems to benefit nobody except the lawyers.
A friend of mine was unable to release her investment in her home with her ex-partner for 2.5 years because he had moved his girlfriend into the house in breach of the Trust Deed, and was excluding her from the property. He pulled out of the sale of the house to a 3rd party for no reason in August 2010, then used every trick possible to prevent selling or buying it himself, until such time as my friend was so desperate, she accepted a very low offer from him in December 2012. She invoked the Trust Deed, but the legal costs were horrendous, and even though the court eventually made an order, her ex- simply said it was on the market but not selling. She had the largest cash investment in the property, yet the law has allowed her ex- and his wife to come out the big winners.
If he had stolen £100,000 from her, it would be a criminal offence, and he would be prosecuted. This was legal 'mugging'! How can that be justice?
A number of her friends just could not believe she was telling the truth about what was happening to her, because her story seemed beyond belief to most law-abiding people.
This story and your situation are very common, and there needs to be a public debate about this, especially with the recent changes in legal aid. Usually, it is the woman who suffers at the hands of the more financially powerful man (as in my friend's case). This is something a newspaper e.g. The Daily Mail, must take up as a campaign (I have written to them but had no response) because it is scandalous.
My friend 'owned' a house but had no regular income, and was therefore excluded from the legal aid system. Her ex- was earning £10,000 per month as a freelance 'consultant' to Lloyds Banking Group and could afford expensive legal action. Today, justice is available only to those who have no money or property whatsoever, and those who have sufficient money to instruct lawyers.
As a footnote, this couple is now being investigated by Bath Police for fraud against my friend in a different matter; something they have tried very hard to hide for 3.5 years.