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Re (from Post #1
"I have had my ups and downs dealing with this ... I know that being with him makes her very happy and has helped take away the depression and loneliness feelings that she had before and I really like that ... but then the thought of them being intimate in a way that I'm not involved in makes me hurt and sometimes jealous ... especially since we have had some very rocky times recently while I was trying to adapt to this new reality and we have become more distant with each other due to me freaking out and her not knowing if I'm going to stay or leave ... so much so where although we get along great in most aspects of our lives together, our sex life has suffered because she has lost a lot of that 'connection' feeling with me."
Sounds like a vicious cycle. You feel insecure and freak out, which puts a damper on your physical intimacy with K, which possibly adds to you feeling insecure, and then soon you freak out again, and the vicious cycle continues.
You and K need to get some more of your connection back. It is the responsibility of both of you to try to make that happen, to break that vicious cycle. I hope you can talk and get some things worked out. I know this isn't the dynamic you originally planned on. You originally expected more of a threesome situation. But, sometimes things turn out differently than we expect.
Perhaps you can negotiate some kind of compromise. K gets some of what she wants; you get some of what you want. You have to both be willing to give a little in order to get a little.
You need good communication. You both need to be good talkers, and good listeners. You need to express your concerns without blame, and be willing to hear her concerns without thought of retaliation.
As you continue to post and read on this site, it will help give you more ideas of what to do. I am certainly pulling for you, as I can hear that this is a difficult time for you.