what should I do?

So for the past 3 years I've been emotionally invested in a man other than my partner of 17 years. Unfortunately this man was his best friend. That changed but it's not specifically related to our "emotional affair". I made a promise early in our relationship that if I ever had feelings for someone else or a genuine interest in another person I'd tell my so, let's say his name is Jack, before making any decisions. I was true to my word. About 4 months had passed and the the best friend (I'll call him Kevin) and I slowly became close. I realized my feelings were no longer just friendship. I sat down with jack and he asked me very directly did I have feelings for Kevin? I admitted that I did and that I thought I might love him. Jack said, "Kevin has feelings for you too but I understand. You are the two people I love most in this world how could you not feel something for each other?" I felt relieved and talked to Kevin later that night about my conversation with Jack. Jack was busy and out of town a lot. He'd depend on Kevin to handle things around the house and deal with issues that might pop up while he was gone. I can't count the number of times jack would say he was busy go ask Kevin. Middle of the second year Kevin went to prison for revocation of parole. I don't care that he has a rather long criminal history it's all drug related. Prior to this last year all for distribution now he's also been convicted of possession of meth. I'm sure for personal use. That was one of the friendships killer between he and Jack. That even didn't sway my feelings for Kevin or the fact that he's spent off and on the last 2 years in prison for the same charges. he'd be released and then fail a drug test back he'd go. I wrote him every couple of days for the entire time he's been gone until this last arrest. A few days before it happened he finally told me that he loved me... Not a vague I have love for you statement. Then he was arrested again and sentenced to another 2 years. I did not send a single letter and told myself that I he loves you he'll write to you. He was arrested in early August. Today I got a very short note from him saying he was just saying hello but didn't want to cause any confusion. He signed it love always, Kevin. All I want is to write him every day and wait for him to come home. I want to run away with him. Even knowing he'll likely always be addicted to some drug. While he's been gone jack and I have had a child and now another on the way but I don't feel the strong love for Jack that I feel for Kevin. I never have. I won't put my kids at risk but I am honestly in love with this man. what should I do?