My husband was married earlier and during that time purchased a house in joint name with his then wi

My husband was married earlier and during that time purchased a house in joint name with his then wife. She was a house-wife, so the EMI was paid by my husband and the EMI still continues. We are unable to sell that house as it is in joint name. Presently, we need to buy a new house. But my husband doesnt trust me, even after 6 years of marriage. He feels that after buying a house, I too may divorce him. My husband doesnt have much money, as he gives away all his money to others.

So, I too have to contribute. But still he is unwilling to buy a house. So I suggested that after finalising on the house, we will enter into an agreement specifying the amount of investment made by each and in case of divorce at a later stage, we may agree on each's share. However he says that in case of divorce if I say in front of the Judge that he has made me sign the agreement by force, the said agreement will be void. So, kindly guide me : 1. Whether the said agreement will be valid or not, in case of divorce. If not, what is the other option. 2. If we want to sell the earlier house which is in the joint name with his ex-wife, what is the recourse.