Be gentle with yourself and don't feel bad if tandeming doesn't work for you.
I have a 2yo who still nurses 4-5X a day and although I'm not pregnant, I at times have the heebie jeebies from him nursing along with the desire to scream "GET OFF ME!" And I have adored nursing him for the past 2 years.
Your body is gearing up to focus on a new baby so to a certain extent it's normal for your body to want to push this one "out of the nest" of nursing.
I'm hoping to get pg in the fall and I really don't want to nurse while pg although I accept that there may be some overlap. I've been doing "don't offer don't refuse" for about 6 months and it hasn't made a whole lot of difference. This kid LOVES his boobies.
My DH is a teacher and will be off school in a week so we are going to actively try to wean him this summer. I don't sit down a lot during the day because that is a nursing cue to him. I push a sippy of water or milk on him a lot so he will stay hydrated because thirst is a nursing cue also. I will let him nurse for a short time during the day and then offer a drink or snack he likes. I am making sure he has enough cuddle time with me during the day because nursing fulfills his need for physical contact. My DH is getting him after naps because he likes to nurse right when he wakes, but if daddy gets him then he gets distracted and sometimes forgets about boobies.
We currently co-sleep, but I'm working on moving him to his own mattress in his room so I'm thinking that may help with his 4am wake up for boobs.
I want to go slow and respect his needs and make sure he doesn't feel rejected. However I realize that with his personality, he would NOT be a good candidate for tandem nursing. I also am having more nursing aversion with him as of late and it's a horrible feeling.
Good luck and don't feel guilty about whatever you decide. I'm sure you're a great mom. You have to do what works for YOU.