Talking about sex, morally sinful?

[boreal]

This would be my concern. An overly scrupulous person tends to project their own hangups on others. You already have him telling you that YOU need to go to confession because HE feels guilty for what sounds like a very necessary and moral conversation about sex. And this was just a conversation! …

This would be a a red light for me in your marriage prep, and something to take up with him and a spiritual director. If his view of sex is malformed, it will not suddenly rectify itself once you are married and sex becomes “legitimate.”

I agree. This is a major red light.

As for the arousal when talking about sex, this has to be carefully balanced with the need to talk about sex before marriage, and the NEED to be sexually attracted to each other before marriage (in our culture …). So the point about talking about sex in order to be aroused is correct (that is something to be confessed), but it sounds like this may be a case where sexual attraction is viewed as a problem that requires confession – and that is dangerous for both the partner and the children.

Very, very boggy ground here… you are supposed to be attracted. A serious and honest conversation about the WHY of the confession suggestion is likely required.

As others have suggested, it may be a good time to seek out a good priest who can help you, and then the both of you together, to tease this knot apart.