Hello Cadbury,
ugh, this does sound hard and you did well even though you have to feel lousy when you see tithead...
My guesses as to why you feel lousy even though you did well:
1. you had to see him at all
2. before you broke up, you both could pretend you were relating, but it wasn't relating
3. now you
know the two of you pretended, but even with this knowledge you must still play a role, not be yourself and it's exhausting. You have changed, but he has not. He's exhausting for another person to be around whether or not the other person is healthy or not. You've changed, but the two of you still cannot relate because this is an impossible task for him. (I still work on this one when I see Nfather...)
4. You want to immunize A against the unhealthy atmosphere tithead presents. Who would knowingly expose their baby to radiation? And yet you are required to do so...that would make any caring mother feel icky.
I think he gave you the money because nothing else will keep you "hooked". Good! He's getting the message that you mean business. He'll probably hold back just those last few dollars when he figures it out. I'm glad you are rejecting his meaningless stupid presents.
If he asks you some other provocative question, just toss the question away. You can tell it's irrelevant when it confuses you whether it's better to answer yes or no. Just say "irrelevant". Pretend (since we're still pretending) that you are a defense attorney. The courtroom game is based on whether questions are fair or not, asked appropriately or not. So think "Objection!" "Sustained."
Perhaps it will help you to know that A is a strong and resilient baby. All the time you spend with him makes him that much stronger and healthier for when he has to deal with adversity from any source, including dear old dad. IMO, that's the part of you that is still vulnerable to this creep. If you can find a potent shield, then you won't feel yucky. And I like what Hoppy said: stop grading yourself! But if you still need to grade yourself, measure your progress by how quickly you and A bounce back after the visit.

You still rock, girl! Hugs, MP