How do I respectfully stop talking to a girl as she now has a boyfriend without being rude about it and losing my self respect?

I (22M) recently met this wonderful woman/girl (23F), we’ll call her Mandy. So Mandy and I met around the beginning of 2020 and we went out only once just before Corona Virus shook the world. We had a great time and planned to meet again soon as things normalized. Now we were talking normally during the lockdown period no problem there. It was only until she started posting on her whatsapp that her crush likes her back and she so happy that I realized there is no reason to for me to keep on talking to her as she has a man now. I was happy that she was happy but deep inside I felt some pain from the disappointment and realization that she’s taken now. We spoke and even planned an outing in a few weeks but I know very well there’s nothing for me there. So I’ve been considering cutting all forms of communication with her but I’m not sure how I can do that in a way that won’t be ghosting and most importantly in a way that preserves my self respect as well in terms of not giving too much of myself away. I’d also like to point out that I acknowledge the fact that it’s totally my fault that I feel upset because she’s in a relationship with someone now hence I need to do myself this favour. I don’t know if it makes sense but I need to remove Mandy from my life without disrespecting her or myself. And I need your help and opinions.