Just to add to Lola123’s reply, whilst it is possible to make a claim against a deceased’s estate on the basis of being a dependent, it is potentially very expensive and time consuming. Also the legal costs incurred by the estate in relation to the claim can effectively reduce the pot of money available to all.
Unfortunately without a will in place, if your partner died, his wife and all the children would inherit and unless you make a successful claim, you would not receive anything. Similarly if you were to split up, you have no right to any financial support.
It is therefore really important that you seek appropriate legal advice and your partner puts a will in place. Also, it would need to be considered how he owns the house with the wife. If he owns is as what is known as joint tenants (as opposed to tenants in common), it would pass automatically to his wife. On the assumption the house is his main asset, that is therefore an important consideration.