(((((((((((hugs)))))))))))))
Firstly, does he wake only to use the toilet?
If after using the bathroom he just automatically gets into your bed then you will have to consistently take him back to his own bed and tuck him in, give him a kiss and go back to bed yourself.
I know that you are tired, but the second he gets wind that you are a pushover and will let him come into your bed then he will try it all the time, but as soon as he realises that he has to get back into his bed then perhaps the novelty of going to the toilet ever coupple of hours will wear off.
Walk-in Walk out is a method of showing children that we will be there for them when they need us but for now they must go to bed as it's time to sleep. If he cries for you, go in, check all is ok, then leave the room. If he cries again, count up to 15 then go in, when he stops crying go out again and so on.
Night wakings can be traumatic, I know, not so long ago I sat on the end of my bed listening to my LO crying for the 10th time(Ithink) with tears streaming down my face as I thought that I was going to strangle her!!! Thankfully I didn't and we are all fine now and getting a good nights rest (mostly) Please hang in there whatever you think will be the best method, please be consistent, how ever hard it might seem now, it will be worth it in the longrun.
PM me if you need to, I will try to help with whatever you decide to do.