I have never witnessed Andrew/Roland/Neil but I block numerous tags, including that one and its variations on A03 to save myself the anger. Aaron/Neil/Andrew, Andrew/Riko/Neil, Neil/Jean/Andrew, Andrew/OMC/Neil, Andrew/Kevin/Neil and all possible variations of ships listed above are also all blocked. I also block tags such as Cheating, Breaking Up & Making Up, Open Relationship, etc., unfortunately some people do not know how to tag properly.
I agree Neil would never want to date Roland (demisexuality aside - but a lot of people who want to use Neil as a Fandom Bicycle tend to ignore his demisexuality). Like you said if he found out Andrew was in high school when him and Roland first hooked up, he's not going to want Roland anywhere near Andrew. Also, if Andrew saw Roland hooking up with high schoolers when Andrew himself is in his 20s and realizes just how young 17 is he'd have a very ugly realization.
Admittedly, I don't trust fic characterization that ignores Neil's rampant canonical jealousy for shipping purposes. Neil is canonically a very jealous person, he literally spends the entirety of TFC telling the reader how jealous he is of Kevin. Part of his jealousy is also Kevin's dynamic with Andrew, which he wants for himself. He wants the fierce protection Andrew displays to Kevin (and Neil is awarded by the narrative at the end of AFTG when Andrew turns on Kevin several times for Neil. Congrats, Neil, he's yours now!).
Andrew is also canonically a possessive person (Nora said in the EC that if Andrew ever suspected Neil of finding someone else attractive (not that he would, Nora also said he only has eyes for Andrew haha) he would immediately tell Neil that person is ugly. Nora also said that if someone other than Neil tried flirting with Andrew, he would be rude & dismissive to them... my man is LOYAL. As soon as he has Neil, he is uninterested in anyone else.
Additionally, Andrew is shown to have what may be categorized as a potential form of hyper-attachment that is common in frequently abandoned children (nearly killing himself to keep Cass, his deal with Aaron that is literally a co-dependency pact, his canonical view of Bee as a 'mother' figure despite her being his therapist, and the fact that he would, according to Word of God, completely lose all joy and desire for human connection if Neil left him or died). Andrew is not leaving Neil or risking doing anything that will prompt Neil to run, there is a reason Nora says one of their versions of 'I love you' is telling the other person to stay: stay with me, stay where I can find you. Fanon!Andrew is often characterized as someone afraid commitment b/c of misinterpreting his "I want nothing" speech. Andrew is not afraid of commitment, it's that he knows when he commits to something he will commit so hard he is willing to die for said commitment.
Furthermore, I've mentioned this in another post, but it's far easier for someone with Andrew's childhood & adulthood sexual trauma to be in an exclusive sexual relationship with someone he can trust to respect all his boundaries, than to risk being severely triggered by unknown variables (and this is why I hate Fanon Playboy!Andrew bc it ultimately ignores his sexual trauma).
* Also, I know Andrew/Neil/Kevin is a fan-favourite b/c it was considered in a previous draft, and some ppl read AFTG and think they can still see its ghost in the pages: I disagree. I think Nora did such a good job cutting out Andrew/Neil/Kevin in the final draft, that by the end of TKM it'd be detrimental to Kevin to try to insert him into the Andrew/Neil relationship. If anyone is interested, I'd be willing to explain my thoughts on that further but I know it's a sensitive topic for a lot of fans.