why is my boyfriend changing with me?

Of course you don't understand it - he's almost twice your age. He doens't know what you are talking about . . .

He liked the chase and now that's over. Plus, you now have nothing in common.

It's over for him.

I suggest that you try to get another job. This is going to make you miserable. Please learn from this very painful experience.

Way back when
In sixty-seven
I was the dandy
Of gamma chi
Sweet things from boston
So young and willing
Moved down to scarsdale
Where the hell am i
Hey nineteen
No we cant dance together
No we cant talk at all
Please take me along
When you slide on down

Hey nineteen
Thats retha franklin
She dont remember
The queen of soul
Its hard times befallen
The sole survivors
She thinks Im crazy
But Im just growing old

Hey nineteen
No we got nothing in common
No we cant talk at all
Please take me along
When you slide on down

The cuervo gold
The fine columbian
Make tonight a wonderful thing

No we cant dance together
No we cant talk at all

This is why people say not to fool around where you work. You say you knew that.

There is a power balance between bosses and assistants. If you go for it, as an assistant, you set yourself up... most of the time.

I suppose once in a while it works out - Leona Helmsly? But also on occasion with people who aren't primarily users.

On some rare occasions, the connection is serious, just fine between grown ups.
But the power balance situation is prime for abuse.

I meant power imbalance.

So, is he married too? (Wake up, smell coffee.)

he is diverced, he is been single for 4 years

Well, good, you avoided that quagmire.

There are reasons people don't fool around with bosses, and even more reasons, like lawsuits, why bosses don't fool around with employees. (Not that no one does that.)

There are famous phrases for fooling around in the workplace, such as "don't **** where you eat." It's generally not professional and can be quite stupid.

That post of mine ended sounding harsh - I'm not all that harsh to you, cuban1ta, and had edited a sentence or two.

He's gay.

If you guys have had sex, then that was all he was after.

If not, he may be feeling guilty or odd about your age difference.
And he may just be a real mean man who , instead of just SAYING he isnt interested anymore, he just wants to lead you on.

One way or another, this does not sound like it is good. He sounds very selfish and unsure of what he wants. No matter the age of a person, if they behave this way, you should not spend a lot of time with them. He may be cheating. He may be dating someone else. He may have been found out ... who knows.
But what IS obvious is that he is not talking to you about what is going on in a way that makes you feel good, and that behavior is hurtful and selfish.

If possible I would look into another job and get out of there. If he chooses to be mean to you , as a boss, he can make your job hard or fire you with out any warning.

Have you not seen Bridget Jones?