The question that you ask is very vague without many details and so ther can be a host of problems that can be causing the lack of sex. Lack of sex does not neccessarily mean that he will ejaculate sooner.
It is quite possible that your spouse could be having an affair, but at the same time is even more possible that he is experiencing andropause, which is similar to menopause.
A further possibility is that he is suffering from a low self image due to impending impotence, penis size issues or performance issues.
I would really recommend that you view the above links, and then have an open discussion with your spouse, and you may be surprised to find out that the problem is probably not a cheating man.
