Have you even played SG?
First of all, his dick works fine, but unfortunately it only works in one direction - Summer's dead pussy.
Second, Nami, roleplaying Summer, was able to make him get a boner.
Third, when the MC allowed Nami to move her buttocks on his dick in jacuzzi, he suddenly discovered that his dick was alive again. So, it's not just dead Summer's pussy that's actually working.
Four, the game doesn't yet say what exactly caused his panic attacks, but now they happen quite regularly. The more body contact he has, the stronger the blow. He lost in the college hallway surrounded by a bunch of girls, he had a panic attack. A threesome kiss with Vic and Mila - he had to retreat to the bathroom and experience a panic attack. He was having fun at a book club - panic attack. Do you really think getting more intimate with Bella is a good idea until he deals with this shit?
The game kinda hints that this idea is not very good. And it seems obvious that until he and Amber visit the damn cabin, he will not make any progress in solving this problem.