The ultimatum your mum has given you is completely unfair, If you don’t want to marry him, she should not try to force you. If that’s what is making you rush and trying to convince your current bf, I understand. But at the same time, have you told him this? If he knows and he is willing to let you marry someone else, then I think that tells you how much he is willing to do to keep you in his life.. basically nothing. I would tell your mum that you aren’t willing to marry this person but also maybe not rush into marrying this guy espec if he’s reluctant, as the saying goes ‘if he wanted to, he would’.