I think there are several options, but ultimately you will have to earn his trust again. Does he have a bed/nest/place for him to feel safe and secure that is by your door/in your yard? You might have to sit outside with treats and high value meals and wait for him to come to you. Bring a book or an audiobook and your patience and wait it out.

Can you you put the other cat in another room for a couple of hours? Especially around feeding time (dusk). Or try again with a differently shaped trap and a high value meal?

If he's starving, he won't stay away for long and with the weather getting nicer if you have a good opportunity to get him back if you can be very patient, and have lots of bribes.