Is your female Sim financially stable? Because sometimes the male would refuse to marry the female if she is not economically stable. I once had that problem with my single mother with two sons who wanted to be an actress but was making minimum wage. It was kind of frustrating. That's why I now like playing The Sims 2 and 3 since they are easier to control. But try that and see what happens. It worked with me (the kids got sent to military school since they were doing so poorly in school and she was able to get back on her feet with money). Also check the personalities of your Sims. Sometimes some negative ones who are mean or grumpy or whatever are less likely to say yes when they are proposed to.
