>“How could you keep it a secret from me”

Its your decision what information you make known to anybody. That doesn't make everything you don't say a secret, just private. She is not owed all and every piece of information about your history because of the nature of her relationship to you. Absolutely OK and understandable to keep this and other things private imo. You are still allowed to be an individual in your relationships.

>“How could you allow me to sit in discomfort and suspicions for this long”

If she was feeling discomfort, its on her to voice it. It makes no sense to remaining suspicious if you haven't even tried to ask the question.

>“How could you be alone multiple times with past partners and think it was okay”

I think its OK. I think it comes down to personal boundaries and trust. If you don't have it, you don't have a stable relationship. You were holding up your end of the monogamy deal. If she doesn't trust you, that's on her.

>All her questions were justified, all her emotions valid.

Ehh, valid is a strong word. I would say they are understandable, but there is too much projection of her own insecurity for this to smell valid to me. I certainly understand her shock and hesitance to ask and accept the situation, and you could have seen it coming and headed the problem off differently, but I think cutting contact with two good friends because of a partners insecurity is always the wrong move. Pushing people away for the benefit of others is how men end up alone. Think of yourself first.

>If Sabrina doesn’t come back and I remain close with Jake and Lena; what happens if ever I enter another relationship? Do I lie for longer?

You didn't lie the first time. But you can certainly see now how keeping your information private that you know will cause pain in the future is not the best call. Just do it sooner before it becomes a big shock, and probably maintain stricter personal boundaries. I operate on the principle that if someone knows enough to ask a question, then they deserve to know a 'complete enough' truth. How complete is up to my (high, I think) moral standards, as long as it isn't so incomplete to be misleading. Your situation is not something I would reveal on a first meeting, but pretty soon after compatibility is established to give them the opportunity to judge if it is compatible with their standards of what is acceptable behaviour/boundaries in their relationships.