There's no difference in meaning between the two...
1: We still saw each other a couple of times a month
2: We were still seeing each other a couple of times a month
The only difference is that the reference/relevance/narrative time has subtly altered. In both versions the meetings being described are in the speaker's past, but by introducing the past progressive, #2 has expanded the "potential scope" of that past. Consider...
1a: ?We still saw each other a couple of times a month when her mother died
2a: We were still seeing each other a couple of times a month when her mother died
I've put a question mark against #1a because I'm guessing many people would agree with me it doesn't work if the intended meaning is "at the time when". You could "fix" it by replacing "when" with "after", if that's the meaning you want anyway - but for my purposes here, I want it to mean "before, at the time when, and after". That's not something you can really do with the simple past as used in #1.
Effectively, using past progressive expands that "reference time" in the past, so it can encompass other events that might even have their own chronological sequence...
2b: We were still seeing each other regularly when first her mother, then her father, died.