Well, from what you have said, your dad could
indeed be bipolar. The spending and the affairs are both red flags. The guilt following the affairs
could have been cycles into depression. The Zoloft could have kicked him into a
really bad mania where yes, a person can think and behave like a total stranger. However your reasoning about the affairs/guilt is perfectly reasonable for someone who is not bipolar, and so with the divorce crises you mentioned. It would be more telling, had you witnessed, in the tumultuos marriage, some of the other sx i listed, specifically during the times of the affairs... and whether the spending coincided for instance.
Annnnnyway, the more important would be if he is still messed up, to get him into treatment, for whatever the "mess" is. If someone is in touch with him - to persuade him to see a pdoc, who could evaluate him in person... but getting him there could be a huge undertaking, regardless what his "mess" might be, even psychological. that is all the advice i could offer, but i fully understand that it might not be realistic. And
here I close off my prying questions and ad hoc suggestions. (thank goodness eh? waves crashing threads and going on about bipolar... sheesh!!!

)
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Up a whole different alley, now. I have noticed your mood consistently says "lonely" and i have felt so lonely myself so many times, i really feel for you. loneliness can be so deep and powerful. So i want to give you a huge hug. there is a nice HUUUUGE smiley hug i reserve for such occasions but it is animated. It does not flash, but it does move. so i don't want to risk posting that here.

howevvvvvver...
(((((((((((((((((((((((((((((( Sue ))))))))))))))))))))))))))))))
that should be seizure-safe!!!
wishing you relief from your loneliness, be it finding moments of peace in solitude, or finding others to share and laugh with.
Sweet blessings to you, Sue, and an angel to watch over you.
~ waves ~ wishes you a wonderful, seizure-free day!