The Sex....or lack of??

Through 16 years of knowing Rob, the sex went from intense to non existant.
Again at this point I can only assume(and proven a few times) that Rob was getting off with others, in person and on the phone.
I recall one time, just to see what would happen, I found an ad in NOW magazine.
It was in the back pages, where escorts posted their ads.
I saw an ad for these 2 guys who would allow you to watch them or partake in sexual acts. To egg Rob on I showed Rob and read it out to him. I half jokingly said we should call but we didnt.
Rob on the other hand, after leaving my place, went home and called.
How do I know...this was still in the early years and I was calling his voicemail.
About a week after I told him about this ad, who had left Rob a message?? One of the 2 guys who posted the ad and again I confronted Rob. Shock and slience was how he reacted.
In the beginning sex was rampant as inany relationship. We didnt perform the act of penetration until about 5 years into our relationship. At that point I thought, he's been committed to me only and took the plunge, literally. Sex had a whole new meaning at that point for me. It was almost like the ultimate bond with someone, someone special.
You would think that someone with a colorful past(and present) past as him he would be adventurous. Unfortunately that was short lived, with me at least.
I remember having sex in the toilets of the Metro Convention centre, almost getting caught by the cleaning crew - Having sex in my bed as my best gal pal lay asleep onmy sofa..he was exciting then. He became more and more or I should say less and less intersted in sex with me, and just me. I understand sex lives change, but to got from rampant sex to nothing was a bit odd to me.
In the beginning of my relationship, I was under the care of a therapist who had me on prozac. One of the side effects was a lack of sex drive and yes I did have that side effect, briefly. I recall Rob quetioning me once, even getting angry at me, and I explained. As I say that soon passed and I was back to my normal "randy" ways..some of the stuff I did with that man still amaze me, that i would do such things, but I aimed to please my then partner. Whatever got him off was hot to me.
Rob is a bottom, and Im vers. There were things, normal things Rob would not do.
He was more into oral and mutal gettin off, until I took the plunge and I got into more and more things. It was odd when we would go on vacation and we wouldnt have sex. The one time couples get all sex crazed is on vacation, in a strange land, in hotel room - not Rob.