他对她有很强的占有欲 = He treats her as if he owns her, demanding total attention or love.

占有欲=占有的欲望。“占有”的意思就是：这是我的！

Literally, it means 'a desire to possess'. Its actual meaning depends. We can say: 那个男人对女人的占有欲很强。That man has a strong desire for women.-->Sexual Desire 他的占有欲很强，很想得到一切美好的东西。He has a strong desire to possess everything good. So it does not necessarily mean the desire to make love.

give the sentence where you've found it

占有欲：Desire to Monopolize