Relationship Advice Please...

SunKissed1989

For the last month, I've been in a relationship with a guy I've been really good friends with for nearly 7 years. I'm 25 and he's 43 - this isn't an issue for either of us as we are both very happy together, we have the same interests, values etc and we love each other very much. However, my parents (especially my mum) don't approve of this and, recently, my mum has gone so far as to say that a mutual friend of me and my boyfriend's (and a work colleague of her's) has come forward with concerns about our relationship saying things about him that aren't true and are quite damaging to his reputation. These rumours are just that: rumours with no evidence to back them up. Our mutual friend has also claimed that he never said anything of the sort to my mum; that he said it was good news that me and my boyfriend had gotten together and my mum just shrugged the comment off (she's never hidden her disapproval).
I want to confront my mum about this, however, I don't know how to go about it as the conversation becomes very awkward and, at this time of year especially, I don't want to cause a rift between myself and my mum (even more so given her opinion on my relationship). Anyone got any advice for me?