Thank you for contacting Just Answer. I am very sorry to hear what is going on. Let me ask you a question. How old is he? I will presume since I don't know his age yet, that the not having sex for two years is not because of his age. Correct me if I am wrong. If we can rule out age as an issue for not having sex in two years then, of course, a different action must be taken. I can imagine, given all that you have said, not only not having sex for two years, but needing to work late, not calling you anymore during the day, not wanting you at his office anymore AND talking to him about what is going on but he denies it and keeps doing it would make you wonder what is really going on. You sound like a sensitive and intelligent woman and are so right to be questioning what is happening. Since he does not talk to you about all that is happening it sounds like a very wise step to have him followed.
I do want to add this --- you need to be prepared to know what you want to do based on what you will find out. How will you handle the outcome, that is. I just want you to think through the different steps and how you will proceed depending on what you will find out.
I see that you are offline now. I'll check back again later to see if you have come back online so that we may continue with our chat if there is anything else you wish to discuss.