My boyfriend is overthinking about his penis and I don’t know how to help

So this happened almost 2.5 weeks ago, but we were having sex, and then midway through his penis went soft. I get it, things happen, I don’t care because it’s happened in the past and we’ve never found it to be a big deal!

BUT,

Now he’s saying it’s affecting his self confidence, and he’s not being as affectionate anymore and I feel like his vibe is totally different.

Is there anything I can do or do I just let it take it’s course? It’s just affecting so many other aspects of our relationship and I have no idea what to do HELP