Ending a friendship?

I met a woman online 4 years ago for a group for moms who are raising biracial kids. We were both going through bad break-ups at the time and kind of commiserated with each other. I met a new man and we have subsequently bought a house and moved in together. My friend is a very negative person and ALWAYS complaining. I recently got off anti-depressants (within the last six months) and feel like all she brings is negativity into my life. Worse yet, she doesn't like my s/o and badmouths him whenever she can; he is just over it. I think she is jealous or whatever bc she is still single and fairly desperate to get married/have more kids. After much thought, I have decided to end the friendship (consists of talking and emailing daily, we live in different states but have met up before) What is the best way to go about this? I feel really bad but feel like I need to work on "me" if you know what I mean, without the whole "misery loves company"