Trying to have sex

There's basically nothing that's completely irreversible... I struggled with DE(delayed ejaculation- in my case complete lack of ejaculation through anything except masturbating to porn) for about 4 years and it took me about 60 days till I was completely "cured" and able to orgasm through normal sex. I don't know if you can compare this to your situation but it sounds like your girlfriend shouldn't give you handjobs or "hard-grip blowjobs" so your penis can get sensitive again. Hard thing is to withstand the urge to let your gf jack you off or smth like that. Just cut off ejaculation completely for a while. Its also related to dopamine levels so best is you just cut off some things that make you instantly happy (like alkohol, cigarettes, drugs, social media etc.) And do a healthy amount of sports. I guess in the worst of all cases, 90 days without a relapse will eventually do it.
Wish you the best luck!

 

Give up the HJ and BJ, at least for now. I'd say give up HJ completely, other than maybe in foreplay. As for how long until you get/stay hard? It varies from person to person. A hard reboot may help you, even a short one. If you can not get or maintain an erection you just need more time to heal. Keep your (and her) hands off for now.