Mm.I'd gotten the impression that Touko had inserted herself into the relationship between Mayumi and her former fiancee in a terrible attempt to make sure that noone was closer to Mayumi than she was.
I really don't like the implication that having a baby "fixed" Touko in the epilogue; having a baby under those circumstances fixes no one, it just gives the option to break one more person.
Hell, everything about Toukou's resolution in the last chapter seems pretty offputting. I'd have liked it better if she'd left on her own after being rejected, at the very least. It would reinforce the ending theme of "make your own decisions about your life". Leave the former fiance out of the decision, he's not a character anyway.
That way, if the intention is "Toukou made her own happiness with the former fiance", then it's at least what she decided to do. If the decision is to bad end Touko, you can break them up off panel, or just "Touko never contacted me again."