My problem with Megan is that she feels like she was designed for the MC, as opposed to her own person. She's a Mary Sue, and as a result their relationship feels "too good to be true", all their problems were external as opposed to any internal ones. Even if you vibe with somebody really well, there's going to be bumps, maybe not big ones, but ones to at least give you a bit of pause(hell their biggest internal issue was whether Megan was ready to take a chance on their relationship or not). I think the Thrupple scenario with Melissa would have been perfect, it doesn't need to be a huge fight but it could be something that they do have to overcome, to finally get to that point where Megan say "okay i'm willing to try this out because i love you both", but nope she's just accepts it.
I do agree about Megan's death, one she had this great career, and relationship going for her, then you have the fact, that Megan was Melissa's rock, her soul-mate, she had a really shit life, and that was the one person who helped her get through it all, and now she's gone, not to demean Melissa's death or anything, but it definitely feels like the depth of pain is greater on that side. The "comforting scene" was also more powerful because of how real it felt. Most narratives like to use some melodramatic dialogue or moment to represent "healing", but DPC going for that approach shows how much he understands, how powerful simply having somebody there can be. Just knowing that there's somebody who understands what your going through, and is simply willing to be there without expecting anything else from you can be extremely comforting.