Need advice in regards to my 13-year relationship

Suzie Q

Hi, I have been exclusively seeing a man for over 13 yrs now, we have been happy together, although I often wondered why he never asked me to marry him. I wanted to get married again (I was divorced with two children just before I met him).
I hinted around at this, but he never has asked me, I get really sad when I see any thing to do with weddings or anniversaries.

I was married for 11 yrs, and he was married for about the same amount of time and divorced about a year before we met. He kept in touch with his ex-wife in regards to the dogs (he is a vet).
She lives in another state and she has re-married. A long time ago the dogs died (of old age).

My biggest problem is, and what I really, really need advise for is: I was messing around on an old computer he had given my son, and was setting up an email account for him. My "boy-friend" (I think it sounds silly to say "boy-friend when he is in his 50's and I am in my 40's!)

Anyway, I found a email he had sent his ex-wife around Christmas time about a year AFTER we had moved in together...we didn't move in together until we had been in the relationship for about 11yrs. Anyway, I found this email after we had lived together for a year! I just can't seem to get it out of my mind! I wish I had never looked, Ignorance is bliss...right???
Maybe, but it's still ignorance!

I would rather be hurt and know the truth!
What I want advise on is what do I do now?
I really love him, and have obviously invested a lot of time in this relationship, but I want to be the ONLY one he loves (except his family of course!)

Is that too much to ask? Please help me, I have no one else to talk to because he is also, or was, my best friend, the only one I thought I could trust. I feel like an idiot and I feel betrayed.
Should I leave? What are your suggestions?

Please HELP!!!
THANK YOU!