I am glad that you have other things in your life. It’s just your expectations of her seeing you at least once a month sounds like you are relying on her for your social life, is unrealistic.

I don’t know why you say she has hard time saying no. She told you she’s busy. Being busy could mean laying on a couch watching tv. She has rights to be busy with whatever else. Also people don’t need a reason to lose interest. Sometimes they just do.

And maybe she became overwhelmed with high demands and expectations. Sure if that’s the case maybe it would be better she spoke up directly but who wants a fight? Last time a friend spoke to you directly, it resulted in a blow out fight. Maybe she’s avoiding it and just keeps it low key.

I still think you would benefit from finding things to stay busy. It’s admirable that you are seeking friendships but you might need more than that. Or you might need to look for friends who have lots of free time