Possibly Putting down a Pet

Hello everyone.

We’ve had our dog for 4 years now and we love him so much. Out of now where he got really sick. He was lethargic and not wanting to eat.

Took him to the vet and told us he had a fungal infection that could have made it into his brain. She suggested we put him down but we didn’t want to give up on him.

Fast forward to today, my sister was walking him and he started having a seizure for like 1 minute. He was weak afterwards and left us scared.

Called our vet and told us we can take him in and see if Doctor can prescribe antisiezure medication. He’s like on 5 different meds and I’m just feeling sorry for him.

He’s is such a happy and energetic dog to be going through this. I think about putting him down and it makes me feel guilty that maybe I’m not giving him a chance. What should I do? I’ve invested so much money into vets because I love our dog. I don’t want him to suffer and it seemed like the medications were working but how do I know when it’s time to say goodbye?

Is putting him down a sin? I don’t think I have the strength or the right to decide when it’s time (obviously when he’s suffering) but he’s such a fighter and I have faith.

Anyone else been in my shoes?