Life does not always make things easy. You have been handed a pretty hard situation to cope with - as too does your wife I'd imagine. 20 years together is a whole lifetime and not something to be discarded lightly. Breaking up is pretty terrible for everyone.
I have to say you sound sensible and restrained and someone who does care for others and look to your obligations, not someone that needs to feel contempt or dislike for himself. The steps you are taking, remaining with your family, being in contact with a support group and talking with your therapist are all excellent. Have you been able to set out a plan as what to do if the urge to self-harm becomes overwhelming?
I've no idea how one handles sexual orientation in this situation, so will make no comment other than to say I'm sure whatever you decide to do will be considerate on all concerned. Seeing the real you, and being open about it can only be a plus.
Loneliness is a horrible thing, now that you have had this talk with your wife do you think there is scope for a closer friendship there? You both are in a hard situation.
I'm sorry about your dad, I guess parents are human and being of an older generation most probably was not able to make the step you have and accept himself. It sounds as if you are the more mature of the two of you.
On a slightly different note this Forum has a thread called:
BB Social Zone /
The Transcendent Rainbow Cafe - social space for LGBTI members
Where members of the LGBTI community can come together for lighthearted chat. It can make a difference to simply be in a friendly atmosphere. You would be very welcome to pop in there and say hello.
I do hope you can feel comfortable enough to return, talking with those that understand can lift a weight.