I find with my 26mo, if a habit has been in place for more than a day or so, it can take a few weeks to dissapear, so if he has been waking for milk for sometime, then it may take awhile for the fact he only gets water to settle in. Also try telling him his water is right by the bed & teach him to find it himself.
Also he will be well aware change is happening, Mummy is more tired, her tummy gets in the way of cuddles & you might be just that bit more cranky & some activities aren't happening as much. So it could be his way of getting a bit more time with you.
I think you are giving mixed messages by staying some time & then leaving (he has no concept of 10mins & 2 mins) & then taking him back. You either have to stay until he is asleep, which I did with my ds for a period & then things went back to how they were before. Or you have to take him back to his bed right from the start, then putting up the gate & taking it down is just confusing, I think you either leave it up all the time or it is never there.
I think you need to decide to do only one part of the 3 things & stick to it, so he knows exactly what is happening. With our 26mo we have a light that comes on when it is time to get up & he knows he can only come into our room when that comes on (took a week to train him) So if he needs me/dh he is either crying or calls out non stop & we go to him, settle him back & if he gets upset when we leave, we stay until he is asleep, most times a quick cuddle is fine (or finding the lost dummy) & I think he settles because he knows the times he really needs us (sick/nightmares) we stay & hop into bed with him or on the floor beside.
HTH