You need to resolve your marriage situation. A secret tracker would be final straw for me as he obviously thinks he is justified in secretly tracking you rather than forgiving you and working through the marriage problems.
The other guy is a distraction, and quite frankly has been the result but not the cause of the break down. You husband won't see it like that. Hence the tracking. You need to stop seeing this other man if he means nothing to you. It's an added complication otherwise.
Make up you mind want you want to to do ( stay, go, or tolerate the current situation) and assess the consequences of each . You can't just assume he will go and live with his parents just because they have space. Get your financial information together, house value, mortgage, debts, incomes, savings, pensions etc. See a lawyer on your options. Be prepared for huge changes in lifestyle if you decide to split up permanently.
If you are not working, find out what benefits you might be able to access if you or he left the home , and run the child support calculator in his income to find out how much he will need to pay depending on child care split ( or vice versa if he fights for children) Remember also that a lump sum from house sale might then make you ineligible for benefits, so plan ahead for an income to afford to buy somewhere if you can afford to do so, rather than running down savings.
There's lots to consider here