Just because a person is partnered doesn’t mean they aren’t thirsty. I have fallen into this trap before and while yes emotional cheating is damaging, it isn’t complete until the physical act happens.
Work on closure and tell the person, while he is the one you are very much interested in, you want more and would like to meet in IRL, but understand that to make that happen he needs to close the chapter on his current chapter.
The thing is are you friends? Can you talk about non sexual things? Can you break off communication for 1–3 days before responding. If you can do this, then suggest to him you want to stay friends and in contact, and you want him in your bed before you are 80 …. but until he is free ….. friends you shall be.
I so very much hate the social buzz wording that folks will use (breadcrumbing), because it tries to generalize some real and deep connection in a single word. The reality is though, there are people that ruly fit that title like a king/queen, but I believe for most that are good hearted and with good intent …. it really doesn’t.
I do believe given the gender imbalance, women will fall into this trap deeply for now more then men (for now and will get reduced over time as things balance out), because the supply of real and mindful masculine men is very rare. Those women that have fallen into luck with one, may not realize how lucky they are and there will always be women that see this and say … nope I want that more then she does ….