What I can do to extend my stay in my house?

In the divorce, did you and your ex enter into a settlement about who would get the house or when you would have to leave? Or did the court issue an order (e.g. a decree) about who gets the house or stays there? If the answer to either of these questions is "yes," you have to do what the settlement or decree says. If it was a settlement or agreement between the two of you, you can ask your ex to voluntarily agree to more time, but his agreement must be voluntary: you can't force him to change what he agreed to. If it was a court order or decree, you make a motion to the court asking for more time: you'll have to make, file, and serve (on your ex) the motion according to the court rules and you'll need to provide justification for what you've been doing to be able to buy your own home and why you need more time. The court is not required to give you more time, but could choose to do so--the court has the power to modify or change its own orders.
If there is no settlement, decree, order, etc. setting a time frame, then there is nothing forceng you to take the buy out or move out now--you and your ex should work out some time that does work for both of you and enter into an agreement about it, to avoid later confusion or litigation, but until there is an agreement or order/decree, you don't have to go.