M.F.
Until she knows that he is "the one", she probably should not force her son to be with him. he should have mommy alone time, and she can date her new beau and have her son at a sitter's when they go on dates. It is really hard on children to bond with someone, and then when the relationship doesn't work out, the person is gone. It inadvertantly teaches them that relationships are temporary. Once the relationship is serious, and they are contemplating getting married, he should want to take an active roll with this little boy. They should never have to compete for mom's attention.
Just my opinion. I learned it at a kids cope with divorce class when I went through mine.