I think...Mikage might be the best person to Suwako. I dunno. Everyone always ends up breaking up with her, and my best guess as the only reason she has a husband because he was rash and proposed like 3 weeks into their relationship or something. Although, he definitely has to know that she fools around a lot, and he still keeps her.
Suwako went under some intense shit during her life. She's a good person but she doesn't know how to cherish someone yet. Mikage is a good person and knows how to cherish someone a little TOO well.
Not sure how you came to this definitive conclusion. We know next to nothing about her.
It's just speculation, really.
But as someone who knows a Suwako-san in real life, I found ColonialCat's post a bit chilling in its accuracy. It's a very thoughtful analysis, and one I'll get behind readily on a bright day. As bad as this might look, maybe their relationship obstacles are something they'll overcome together, and they'll both fondly look back on these stories as their "rough patch."