Purple:

To a degree I can understand your anxiety and enthusiasm. But girl you need to stop and breathe. For a week you have been running around chasing your tail over this issue.

I think honestly you need to go talk to someone, a therapist or counselor/ clergy and have them help you process this large change in your life.

Unless that 'someone' helping you is a PI who can background check, take two steps back and re-evaluate. Then consider the following:

You just cold called a man that you DONT know, and explained you might be his daughter.. you don't know for sure as mom was apparently going through a very 'fun' dating phase in her life.

Could this guy be innocent? Yes. I have worked in hospital settings with 3 Michael Lipschitz on the same staff. Let alone common names, if its John Smith or something similar it is possible there was one per shift... both A side shift and B side.

But lets suppose this is your Bio-F.

Is he an axe murderer?
Drug addict?
Alcoholic?
Does he have a WIFE he was married to during that period of time, whose 30+ year marriage this is about to seriously screw up?
Does this man have mental problems?
Is he a societal leech who will be happy to 'claim' you... so you can support him.
Is he a thief?
Liar?
Cheat?
Is he running drugs?
A pedophile?
And abuser?
Have alzheimers?
Or a stress or anxiety diagnoses that you just aggrevated?
What if its a heart problem and the stress of this makes him sick?
Or worse one of the two above... and this guy is NOT the baby daddy?

Stop. Think. Use logic, common sense, talk to a professional so you can move forward in your life confidently and SAFELY.

^^^thank you jhw, for your voice of impeccable reason^^^

I understand your nervous and excited at the same time. Who wouldn't be curious? But please realize that you can't rush or force this. I'm really not meaning to sound mean, but the gentleman may not have the same need to 'know' you as you have to 'know' him. A stranger just phoned him and laid a huge blow on him. Just as you know nothing really about him or his life for the last 40yrs, he knows nothing about you. Even if he got to the point of acknowledging it all could be true (even proving through DNA to him), he may have questions or problems trusting why you now want to 'know' him.

Until you learn more about him (the suggestions by just his wife were excellent) he may turn out to be a huge disappointment or he may question your reasons of hunting him down. He may be afraid of what you might want from him (yes, I know you 'want' nothing other than the chance to meet him and possible chance to have a relationship with him...but he knows you as a stranger which may have ill intentions (yes, I know you don't).

There's also a possibility that no matter how legit you are and how wonderful of a person you are, he may choose to not want to meet and accept you. Give him time. I assume you left name and number and he can call you after the shock wears off a bit. Just because he was hesitant the initial call does not mean he's totally closed to the idea. He may be now trying to check you out and quietly learn more about the woman who phoned him. I don't think this is something either one of you should race into. You've been in a tailspin all week. Slow down and remember you just dumped the same shock on him.

40yrs is a long time. He really may not remember your mother or only have very vague recollections of her. If he was dating other people during the time mom had moved and then returned and also still dating someone else after mom returned (aka cheating on her) there's a chance he had multi girlfriends and perhaps even flings with different co-workers. Give him time. Research him. Let him mull it over and research you.

As hard as reality may be, while you did have a right to know, you don't have a right to barge in and intrude on his life. One way to attempt to follow bio-dad's life the past 40yrs would be to go down to the library and search the newspaper archives. Items like marriages, births, arrests, military news blah blah are usually throughout his local newspapers. It would give you a chance to perhaps learn more about him as a man and what his life as been like for 40yrs.

I truly hope this all turns out for you. That he is a nice guy and is willing to meet you and get a chance to know you. It's tempting to want to meet the 1/2 brother and perhaps forge a relationship with the brother also. But know that you know the truth and have contacted the gentleman, the rest is really up to him whether he desires to meet you and get to know you as a person. You know, it's has loss (for the second time) if he chooses to not meet you, but what you can't do is force yourself and a meeting. He has rights and decisions to make also. I'm sure you've perked his curiosity , really the next move is his to make.

I'm going to try saying this as nicely as possible.

You already know I don't think you're a particularly stable person and this, right here, is a huge red flag. You've called up out of the blue and are practically throwing yourself at this man and insisting he's your father and requesting a DNA test to prove it and and and...

STOP.

He really might not want anything to do with you whether you're his "child" or not. Maybe he doesn't want a DNA test because he prefers to say, "Nope, you're not my kid" and doesn't want to be proved wrong.

Can you stop for a minute and imagine what you've just done to HIS life?

Purple, the advice above is what I would follow.
Think about the women here who find out their DH/SO fathered a child before they knew him and now that child appears in their life. Their children are displaced and no longer the 'firstborn' or the first daughter/son. Their whole lives turn out to have huge holes in them.Lawyers get involved. What about Wills and bequeaths from deceased relatives that go to "all of John's children upon my death".

If you approach him again just tell him the primary reason you would like to speak to him is to learn any medical knowledge that would benefit you and your bio children. Then tell him thank you and leave him your address.

He may also want to check YOU out. After all, he can't even remember your mother. Why do YOU want to contact him? Has he recently received a large amount of money and co-incidentally you turn up?

I know you want answers but you need to wait. And try not to stalk the guy!