After spending nearly 20 years with one woman, can a man really go on to love someone else - seems like he is?

institutionalised but says he wants to start with me - just wondering if it is possible he can start from scratch again. She cheated on him so it was not him to end it so I am more than a little wary as it were. He does tend to talk alot about her too - from their wedding to things they used to do. At the minute we have not done owt but be friends - I think he needs a pal just now more than anything else but he insists he IS over her - what do you think?