I reckon it's someone she went out with before Barry that's engaged. She'd hardly mention Barry's private stuff online would she, out of respect for Roisin? Last family photos with Barry are July 2022 on her grid, so they're not even separated 2 years yet. He's moved on very quickly if he is engaged already.
Imagine - she's never been single as an adult if this is the longest she's been single since she was 17. No wonder she can't cope! Might actually do her some good to learn who she actually is as a person before running to the next man.