I must say: you are coming along and accepting things very well
There aren't many people who would be as willing and able to forgive a spouse/lover the cheating and lies while being willing to accept the one who helped the s/l cheat!
You are AWESOME in my book!
Yes, it can be a hard road but the rewards FAR out weigh the negative things.
We have hard times in mono relationships AND poly relationships the difference is that the more people there are in a relationship the more complicated it becomes. You seem to be doing absolutely wonderful! Even with the hard times you are still willing to at least try to forgive and forget! I know a few people (in the mono world, no less) who could take lessons from you on how it should be done, lol.
May your journey be as stress free as possible and may you continue on in this with as much awesomeness as you have already shown.