With friends like Lieseloth (who names their kids that anyway), what do you expect?
Good thing is if you dismiss Mathias he doesn't touch your ass during that scene and it never moves on to a kiss after.
The problem i have with this whole Mathias thingy is that - even if you tell him to fuck off and say you don't want anything to do with him right at the beginning of the game (cause he is a creep and should just stay away).
My MC acts like she had forgiven him instead in the new update, even telling her Mom she had a heart to heart with him and it's fine now, cause he was just in love with her ?
And now she is flirting with that creep like your choice and every other interaction with him before the 0.5 Part 1 update has been ignored.
Sure you can still avoid the groping but it shouldn't even come to this scene (why would the MC in this case even sit with him alone and entertain this whole flirting bs to begin with) if you clearly said you hate his guts and you don't forgive him, it doesn't make sense.
I hope the dev fixes this in the future ...