Thanks for confirming. Firstly, his assets and finances will not be increased if you prove cohabitation, as you cannot seek any of his partner's assets and you can only seek a share of matrimonial assets as part of financial relief proceedings.
Furthermore, I would not suggest you hire a private investigator as even if you proved cohabitation, hiring a private investigator to follow him may be considered by the court to be a dishonest action. The court will not have made a direction for such action and any evidence you obtain cannot be admitted unless a court direction is made for it to be obtained.
Furthermore, cohabitation is if they were living together as husband and wife and her car parked at his property three times will not prove cohabitation.
Given that you are aware of his high income and possibly other assets, you would be best served to focus on these and to ensure that you have fully outlined what your (and the children's) reasonable needs are in order for the court to make a decision that meets these needs.
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