If you get them on the phone, you can try and determine how they are currently feeling by how they respond. Let them take the initiative as to if there will be another date. That doesn't mean they need to directly ask you out, but they do need to indicate they enjoyed hearing a remark from you like "I hope to see you around" or "Will I see you at the game?" may likely be a positive sign.
If no hint of an eventual invitation or opening for one is forthcoming, it is best to let the relationship go. It is possible you may get a surprise phone call or email someday but you can't live your life depending on it. Even if the person was interested and it is simply their internal baggage that stands in the way that doesn't mean they will be able to push it aside to the degree that would make it possible for a relationship to succeed.
If you get a request to 'just be friends,' do go ahead and communicate or have outings with your former partner when and if you can truly accept a platonic friendship. Respect their boundary and do not press for more. It is possible that at some point you may discover what impeded them from progressing further in the dating process.
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By becoming a 'safe' person for them to be around, they may eventually open up their feelings to you in an unexpected way. Then you have information you can work with. Even if you still have a strong desire, do not be physically intimate during this time as you run the risk of just turning into a 'friend with benefits.' Once that happens, it is very difficult for the relationship to ever become anything more.
Infatuations can rise and fall. Knowing the potential for a relationship to fall apart within the first twelve weeks, it is best to never tell someone you love them. This saves your partner from potential hurt and having created expectations you may later regret. If the feelings of love are real, they will still be there when that period is over. After that is the time to evaluate how close you really are to being able to sincerely use the word 'love.'
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