Hello tophtwin,
I think I have the exact same problem as you. I have no trouble getting hard when doing sexual things that aren't intercourse, such as oral sex or hand stimulation. But when I start to put on the condom, I instantly start thinking about failing to maintain an erection instead of how attracted I am to my partner.
As of right now, I've been trying to go without masturbating or watching any sort of pornography for several days in a row before attempting intercourse. We had an opportunity to try again, but she didn't feel like intercourse. However, I did get a very strong erection; much stronger than my usual ones. Hopefully it'll work the next time I try.
I hope you're doing well, and best of luck.