Is it normal for my gay partner to suddenly like young boys?

Here is my story…I am a gay man who has been in the same relationship for twenty years.
My partner is closeted or he still thinks he is even though he does not date women.
Anyway just a little synopsis about our relationship. He and I met on a personal’s service, and instantly liked one another. However, I used to live in another part of the country. We would travel to be with one another almost every weekend until I finally moved where he lives.
Once arriving and getting settled in an apartment he proceeded to tell me we had to hide our relationship for the time being. His dad was still alive and he was responsible for seeing to it his dad got any care he might need.
Well his father passed away after six years of me living in his city. I asked if we were going to live together once his dad was out of the picture. He said he wished we could, but he was just not comfortable living with a man.
Therefore, he bought me a beautiful house for an anniversary gift (it is my house/name on it totally), and I thought he was just wonderful for buying such a huge and beautiful house.
I moved into my house, and once I lived there for three years he asked if I was ready to live with him.
It did seem a bit confusing he suddenly wanted me to live with him because he still had made no attempt to introduce me to anyone in his family, friends etc..
I agreed to move in with him, but I said his house wasn't large enough. Therefore, we went house shopping and found another beautiful house that needed restoration.
Once the renovations were finished he and I got into a huge argument about something, I honestly don’t remember what it was. He decided it would be best for me to live alone in the house we had bought together, and I am still living here.
Well fast forward the tape ten years…he was invited to a wedding for a cousin of his, and his family had finally found out about me.
However, I was not invited to the wedding, and not being invited to the wedding was the end for me. He went to the wedding after I asked him if he would at least ask his cousin why I wasn’t included. He never asked his cousin, and his entire family got together for three days (excluding me) and it was beyond painful.
Therefore, I decided to pack and leave for good…
just a little (FYI) he had told me years earlier we’d have a normal relationship. However, I had waited long enough.
In the meantime while I was packing trying to get things squared away for the sale of the house. He begged me not to leave him, he said he would pay for us to go to therapy if I were willing to go. I had begged him for years to go to therapy, and now I'm walking out the door he’s ready to go.
However, I did agree to go one reason is because my job is working for a company he and I both started together. Although, the company is strictly in his name, and he’s there every day. I figured while we were in therapy I could seek employment elsewhere.
The big shocker came last week in one of the therapy sessions (sorry he is considerably older than me).
I had always suspected he was attracted to teenager boys up to the age of about 22 or so.
Knowing we had ‘NEVER’ had a satisfying sex life is one of the ways I knew it. Watching him cruise guys up to the age of about 22 or so was a great give-away too.
The therapist asked if we had a healthy sex life, and I answered first because she was looking at me.
I said not really, he lacked a lot of passion which I love a lot. She asked him what his opinion of a good sex life is/was or did we to him have a good one.
He answered saying he thought it was OK, and had no real complaints.
However, I was not ready for the answer he gave after his first statement. He said but it might be more fulfilling if R__ (me) were younger (he is 69 & I am 48) keep in mind we've been together for twenty years. Therefore, I knew he liked younger guys.
He didn't mean young men he said he means if I were 10 - 14 year old boys.
When I found out he was attracted to young boys, and the attraction to them is stronger than any attraction to anyone. I don’t know how to proceed in this relationship any-more.
He’s been talking about marriage (believe it or not) and I just want to get away from him. I was molested as a child, and this information is too much for me to take.
What do you think, do you think I should just forget about what he said about the boys, and go forward with him. My first reaction is to leave…I feel like I am being molested over again in a way.
What if anything can I do to stay with him, and try to understand.
Thanks in advance for your help,