op this has happened to me, the most important thing is to take him out frequently to meet other dogs again, and control your anxiety, difficult as that may sound.
If you don't want him to be fearful you have to be confident yourself, take him to meet up with friends who have gentle dogs you know as soon as possible, keep doing it, and as long as the other dogs are known to be safe let him off the lead and walk away.
He needs to find his confidence back.
My Spaniel was very badly bitten ay 14 weeks, and screamed in pain.
Despite my feelings the next day l took him to our dog daycare centre and put him in with the small dogs for 30 minutes, he was scared for 10, unsure for 5 then started playing. I also took him everywhere with me and let him sniff any old/slow/gentle dog l came across.
I did this for a week (all the dogs there were known to be very well socialised) he is now the most confident dog...
The secret is YOU letting go of your fear as he will take his cues from you, to do this find safe dogs for him to have lots of contact with ideally for short periods three times a day. Then you will be confident to encourage.....good luck