The key with a 32 mo, is to tell them what you are doing & not at bed time but at another time of the day.
So say with our son, when we make changes to the bedtime routine (say dh or me not being home) we talk about it during the day & explain what will happen... we have been doing that since he was 2yo
So you start off by saying tonight at bed time you will sit on a chair next to him until he falls asleep & when he is asleep you will go to your own bed... the same will happen when he wakes at night. then when he gets upset, you say "remember we talked about it, Mummy is here... you then DON'T give in EVER, be prepared for some backlash, but the key is for him to learn that you are consistent with what you say & do. Then once he is comfortable with that, you move further away etc... but you can't do it & then cave in, as that just shows him he needs to try harder for you to cave like you did last time.
He is also probably feeling left out by having a younger sibling, so it is also important to give him as much time as you can in the day... get him involved in being your helper in everything possible, try to give him one -on one time, even doing special activities to show he is just as important now the new sibling is here.
In the day time always keep promises when you leave the room & then at night do exactly what you have told him you will do.
When you get to a stage you can leave the room with him awake, make agreements with him as to what you will do... eg tell him you will check on him when you go to bed & do it.
