does he fuck her anyway, even if She suck MC's dick?
Here is the dialog, which you get whether you got the blow job or not:
ni "Let's just say that I've been in love with a girl who doesn't even see me for the last couple of years."
mc "Is that a secret?"
ni "She's in a relationship with someone and there's nothing I can do about it."
mc "Ouch... I've had crushes like that too. It sucks."
mc "You haven't managed to move on after two years?"
ni "It's not simple to do that when she's constantly around."
ni "Recently, I crossed a line I didn't think I would cross."
ni "She confided in me and one thing led to another..."
ni "At Halloween, I ended up in bed with her. We were both drunk and part of me has wanted to do that since the beginning, but...fuck..."
mc "(Is he...talking about Heather?)"
So the inference is that Nick and Heather had sex. If you got the blowjob then Nick elaborates more:
mc "Since you're sharing this secret with me, I'll do the same with you."
mc "Because I can't take it back either..."
ni "You had sex with Heather too?"
mc "Almost. She gave me a blowjob and a titjob at Halloween in Leon's room."
mc "She did it to get back at Tommy for fucking girls without checking with her first."
ni "Yes! That's exactly it."
ni "But she told me that after we already fucked."
ni "She came up to me and was upset about something. We sat down and talked, and she poured her heart out."
ni "I told her how I felt for her and we started making out."
ni "I took her back up to my room and we had sex. She even fell asleep in my arms after."
ni "And when we woke up, she felt so much remorse and told me she did it because of how Tommy's been treating her."
ni "She said that night would be our secret, but I don't think she can keep that. She regretted everything and even cried before she left."
ni "I've felt horrible since. She fucking used me..."
ni "Having sex with her is something I've dreamt of, but it ended up being this big disappointment."
Whether DPC treats the story differently if you had the BJ or not since if you did Nick tells you explicitly they did fuck whereas if you did not there is room for ambiguity.