Hello 0670kb: I see this was your first post here on PsychCentral. I'm sorry no one has replied to your post until now. I hope you will find the time you spend here on PC to be of benefit. The more you post, & reply to other members' posts, the more connected to the community you will feel.
I'm not sure I really have much to offer you in terms of a response to your concerns. It's been many years now since I had similar kinds of concerns. But many years ago, I had some similar experiences. With the passage of time, I think I have developed some perspective with regard to what I did. Yet it still puzzles me. And the fact that I did it haunts me.
Of course I don't know how serious your relationship with your boyfriend is. If, realistically, he just isn't the love of your life, perhaps what you're doing is just a sign that it's time to end the relationship. On the other hand, if he is your "one-&-only" & you're cheating on him, then this is of course a more serious situation.
Personally, I don't think people ever just stop feeling feelings. There's something going on with you that is causing you to experience this lack of emotion. Depression would certainly be a prime candidate. Lack of emotional response, anger & sadness are all hallmarks of this condition. But, there are other possibilities too & in order to figure out what is going on with you for sure, perhaps you might want to consider seeing a therapist. Having the opportunity to talk this all through with someone, at length, may help you to come to terms with what's going on. The important thing here is , I believe, that you take some sort of positive action as soon as possible to remedy your situation. The truth will out, as the saying goes. And when it does finally come out it could well be difficult in the extreme for all concerned. I wish you all the best...