Sorry, I can't help with the finding of a detective service, but you got some good suggestions on how to start looking into it on your own from some of the other moms.
What I can help you with is this: there is more than one way for a marriage to be broken. Our marriage was in pretty bad shape and we've been working on improving it for over a year now.
We've been going to a program called ReEngage at Watermark Church on I-635 between Hillcrest and I-75. It's at 6:30 on Wed nites. It has helped us regain a sense of trust and caring in our marriage.
It would be a long drive for you, but if you and he were willing to do the drive and take the time to do the homework, it might help you reestablish your marriage. You can look it up online by googling Watermark Church and choosing "adult ministries." You don't have to be a member to participate in the program. It's a way to get some help without paying for a counselor. Again, it has helped us - and many other couples - tremendously. It's not a fix-all, but it sure helps you take a step back and look at things and figure out what's not working and how to start the process of fixing it. My husband and I are going through it a second time.
I would stay away from the TV thing if you have any desire to save your marriage. I agree with some of the other moms here - whether or not he's cheating now, you have not developed a sense of trust in him and that's an issue that needs attention from both of you.
Hope you get some relief/make some progress/get some hope!
PS If you just can't make the long drive, then read some books together. His Needs, Her Needs is a good place to start. If he is not willing to read some books together and improve the marriage, that might be an indicator that he's not really interested in a REAL marriage. Currently I'm reading a book called Boundaries by Drs. Henry Cloud and John Townsend. It is helping me to recognize where I'm not effectively drawing the boundaries that protect the inner me. It might help you in some way, too.
God bless you.