where do you find the strength to go on?

My partner has just been diagnosed with ADHD - well...sort of, not really. He was actually diagnosed at 6YO, but his mother never told anyone about it. My psychologist suggested to look into it with him, and that's when EVERYTHING became clear, 34 years later. In the 8 years that I have been in a relationship with him, we have gone through several house moves, him losing his job more than once, he has assumed that we were engaged to be married, a wedding that was cancelled at the last minute, he has cheated on me while I was pregnant with our 3rd child - pretty much our only happy memories are the births of the kids - and even those were under enormously stressful circumstances - and he is now attributing all of it towards ADHD. I feel burnt out, and as though my heart, hopes and dreams are shattered. On top of asking me to miss some pretty huge milestones in my life that I can never get back, AND displaying (what i see as) some pretty bad behaviour for a lengthy time, and whilst I realise that ADHD is a part of that, it's not the full story. He's now asking me to trust, forgive and support him while he gets his life together, probably for the first time. Haven't I given enough? Haven't i put up with enough? At what point do my needs and wants factor in to this? Would i be a cold, hard bitch if I left to try and put some semblance of a life back together for myself?