If you were not married or in a civil partnership then a change in your capital position or that of your partner is unlikely to give rise to any financial claims between you, although it may be possible for you to make further claims on behalf of any children (see if you have children.)
If you were married or in a civil partnership, and either your capital position worsens or you believe your former spouse or civil partner's capital position has significantly improved, then you should check the terms of the agreement or court order made on divorce or dissolution to see whether you can still make claims for capital against your former spouse or civil partner or whether your claims for capital were brought to an end (called a “clean break”) see The financial settlement. If they have not been dismissed it may be possible for you to make a claim. However, the courts are very reluctant to open up agreements. If the change in capital affects the very basis on which the agreement was made then you may be able to take action. You should speak to a solicitor if this is the case to see what your options are.