I am Roman Catholic and it is hard too. I don't have the answer, but also know if I follow the teachings I epically fail "every damn(ed) day".
I believe in God with all my heart and soul, though I know I fail a lot.
I believe the priests intentions and reflections are wrong. If the couple is married and is Catholic, and they are doing IVF that should be allowed, but it should never stop the actual process of love making and sex.
Sex though if I remember correctly is for both procreation and for maintaining the sanctity of marriage. I don't know where that priest got his training, but it sounds like he did not do "well" in those classes.
Honestly, I would find another priest. As for contraceptives, that is a hard one too. If a couple uses them over an entire life time, one might have to ask since the church believes in children as part of having the family, one might have to ask was this the right partner.
That being said, we now live in a new era, where diseases happen (or God forbid) genetic matching shows "bad" things from happening.
It is a slippery slope as for Onan ... that was with masturbation :-), and oddly enough for men in today's life ... maybe there is a salt or grain of truth.
What would guys be like if they limited their masturbation and conversely controlled themselves and focused their sexual energies on men and women? Would they not possibly treat women better?
My advice as a Roman Catholic who doesn't practice, is to find another priest and talk to them. The one you just listened too, seems to have issues.