It's only 3 months, GET OVER IT ALREADY!

Question:

So before u got together with my boyfriend, my ex and I shared a lot of bills. We were together 9 years. Well, he had a Samsung Galaxy Note S8 he had gotten in 2018 January and it's still on my line he pays me each month for it and his service. I explained that once the phone is paid off, he has to get his own line.. My current bf has recently made this a tremendous issue. He has always felt some type of way about my ex and I....acting like I want this man. I left him for a reason. If I wanted him, I could have had him, I didn't so I left. I was unhappy. There wasn't any bad blood, we are cordial. I told my bf last year, it will be paid off in February 2020. I can't understand why we are still having this same conversation. He brought it up last night, today and a week ago. Idk if it's bc I'm pregnant or what. I told him of he wants to pay dude phone off and clear the line for me then, I'm cool with it, but until then I don't want to hear anymore about it. I refuse and cannot afford to pay off that phone. I need to preserve my money as does he. It's 3 fucking months! I want to know am I wrong or is he just being the childish boy I told him he was. I understand his frustration and how it affects him, but he knew this from the start and I could have just lied, he'd never known. But I walkway believe it's easier to communicate the truth than cover up a lie.