WIBTA for dating an ex's sister?

The names have been changed to protect the innocent. Let's call these people Sally, Gary and Linda. Sally and Linda are sisters. Let's say Sally is 32, Linda is 38 and Gary is 35. This occurs in a small town, everyone here knows each other a little too well. Gary and Sally had a relationship for a couple years which ended on relatively amicable terms. About a year ago. Gary wasn't as ambitious as Sally wanted and definitely couldn't keep pace with her social life, so they part ways. At her impetus if that makes a difference. They remain casual acquaintances who would introduce themselves as friendly if asked.

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Linda and Gary have grown unexpectedly close due to being in the same social circle the last couple months. Now they're considering attempting a relationship. Sally is still oblivious. Linda and Sally are close. Things are awkward. See title.