This was maybe a little too subtle and in need of adjustment on my end.
Consider things from Roswell's perspective. He's only seen this guy who's been toxic lingering around someone he cares about. He's not seen anything to warrant that Tyson has changed, just the insistence from Dave that he has. For him, this is troubling because after the month is up, he's scared that he's leaving his friend with someone abusive and that has some level of emotional compromise over.
But separate to that, Dave's not giving Roswell a fair shot of it. He invited Tyson without considering the trauma of what Tyson did to them as kids. Dave also didn't acknowledge that what what Tyson did was wrong, just that he was different and painted Roswell as the villain for not letting it go. As far as friends go, Dave was very much in the wrong for dismissing Roswell's feelings even if they were not the greatest. I feel like Roswell's reasoning here is sound, if still mired by emotional baggage he hasn't let go, and he's justified in wanting Dave to apologize.
Imagine your friend broke up with their boyfriend and you brought said boyfriend to a party as a friend. If the breakup was messy as all hell, is that really all that appropriate?