Hello, this is Jim and I am a dual-qualified lawyer (UK and Republic of Ireland) and happy to help you today.
What you say is correct if you were unmarried - mainly because married couples have more rights and the court can depart from the "£100K to you versus nothing to him" situation if he is much worse off than you, or you have more assets than him (and lots of other factors).
If you sold the house then assuming your husband agrees, you can get the £100K back - this assumes he is not obstructive though. It would help to have an agreement drawn up. As it stands, you get back half of any equity in the house - he may suggest the £100K is matrimonial money used for the benefit of the marriage (hence he may have a right to it).
Like I say, even if you have some agreement drawn up, the family court can depart from that agreement. Yes, your contribution of £100K would be taken in to account but so would lots of other factors.
If you did split up or divorce and ask the court for a financial order, the court will consider the factors contained within Section 25 of the Matrimonial Causes Act 1973 when it assesses a financial settlement.
Therefore your ages, length of marriage, any children under 18, your earnings and earning potential (same for your husband), the assets including the former matrimonial home and pensions if applicable, any debts, financial and non-financial contributions to the marriage (e.g. £100K deposit), your standard of living enjoyed before the marriage breakdown, your financial needs in future and your housing needs, and so on.
The starting point is 50% but if there is a disparity in earnings or you have paid more in the way of deposit etc, you can ask for more than 50% of the former matrimonial home.
I hope this helps – if you can please give a positive rating by clicking 5 stars (at the top of your screen), I can answer any follow up questions at no extra charge and I will be credited for helping you today.