You will both benefit a great deal from therapy, individually and as a couple. What he is going through is very, very hard and scary and can cause even fairly stable people to kind of lose their ->-bleeped-<-, but you have correctly recognized that 1) a lot of this is his baggage that he will have to deal with himself, and 2) you are entitled to be stunned, afraid, unsure, and grieving.
His suicide attempt is not your fault. It is not your fault. It is not your fault. It is NOT your fault.
He is feeling terrified, rejected, alone, and unlovable right now. That's part of coming out for many people, and it's really tough, and it's understandable that he really wants--and feels like he NEEDS--a promise that you will be there and will love him in exactly the same way you always have. It's understandable that he is feeling anguish about the loss of the family he thought he'd have with you, and is desperate to preserve that dream somehow. But forcing you to commit to things you don't want is not the answer. He needs therapy, and he needs to be okay with himself. No matter how tightly he holds you, the things that are hurting and terrifying him are still going to be there, and he will have to deal with them. And in order to have a healthy, happy, loving relationship based on your full and free consent (as it should be), he is going to have to deal with all of that. That work is his own, and he is the one who has to do it.
It is not true that your love is a lie if you can't love him exactly the way he wants. Some people really are exclusively homosexual or heterosexual. If that's who you are, you can't will yourself out of your sexual orientation. I was in a relationship with a man for a long time, and believe me, I tried to will myself into it. It did not work. I cared for him a great deal--nothing about my love was false, but it was not the love of a heterosexual woman for a man. And ultimately, I had to admit that I could not make it work. I gave him what I had to give, but it wasn't what either of us wanted. You are not a liar or a traitor or heartless or cruel if you can't do it. You would not, in the end, be doing him any favors by staying in the relationship and spending each day trying your very best and hardest to muster up the gay love you wish you felt. You can still love him even if you're not in love with him--as a friend, as a brother, as a wonderful person you care about very much. Of course, it's possible that your sexual orientation is flexible enough to include a man, but you've never really given it much thought. That is something you can work through with a therapist, and think about over time, but don't feel you have to have all the answers right this minute.
You're right that it sounds like you're receiving ultimatums and guilt trips. Those are based on his very understandable fear and pain, but you are entitled to say "no" if what he's suggesting is not what you want. The responsibility that you had toward him was to be honest, to respect his identity, and to treat him kindly. It sounds like you have done that. If your relationship is going to survive, you need therapy, time to adjust and work through your fear and loss, and enough emotional space to make a decision that's actually yours.
My heart goes out to you. This is going to be a really, really tough time for you both, no matter what happens. If you decide to stay, I strongly encourage you to check out support groups for non-trans partners of trans people. It's great if you can find a group in your area you can actually meet with and talk to, but there are online support groups as well. Best of luck.
