Why guys play women or take advantage of them?

I was completely taken advantage of by a man I thought I knew and trusted him with a lot, including being around my children. He acted so charismatic and was very persistent in trying to be with me since he has had a major crush on me and still does. I've been a single widow for more than a decade, so I was intrigued and a little shocked. I am also eventually fell in love with him and, of course, wanted more with him. I feel taken advantage of by someone I've known for years and didn't even think twice. How do I move on and not fall for it for a second time? Even after all he did, i still love him and will probably always will.
Why guys play women or take advantage of them?
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