I think it'll happen the same way most ships w regulus happens in that they use him as a substitute for sieius???
Maybe it's after padtail happened and peter has to get his fix from SOMEWHERE so he goes to regulus
Umm so regulus is passed of his older brother (rifhtfully) getting all the attention and so when Peter starts making moves and rehulus thinks "ykw fuck yeah"(except he wouldnt say fuck he isnt cool enuff to) and peter only made those moves bc he can't have Sirius anymore and regulus on some level, understands this but he doesn't care (not bc hes being manipulated, he convinces himself. HES in control) and infant manages to convince himself that peter acc likes him more (peter doesnt said 5his but he knos sirius and yet is in bed w regulus) and regulus finds it sorta freeing bc he can be mean all he wants now (like sirius) and peter wouldn't leave (bc he cant get his srs fix anywhere else) i feel like peter would NAWT be phased bc reguluss bitchiness is inferior to siriuss and peter is manipulative so he says stuff like "sirius would have done this.." ("this" is bouncing on peters dick) and regulus KNOWS this is manipulative he KNOWS but he doenst stop bc well he WANTS to show peter that he IS better than his brother and so...he bounces on the dick
And it couldn't hurt could it? Letting peter THINK he's manipulating regulus bwhen in reality regulus is in control (hes not) ? It couldn't Hurt to ride that dick and it couldn't hurt if he let's peter do those (slightlypainful) temp body mods on him ? Right? Right???
And even if they did hurt regulus could get "back" at him (used to be a slightly effective system in the early days but now it's like peter cuts regulus up and then after peter "lets" regulus get back by like being mean to him and tyelling a little nd regulus thinks this is a fair trade bc he's never been in acc romantic rlnship before)
But regulus is quite toxic too he's never been in a rlnship before and doesn't kno how to act And the only frame for a rlnship is like the ones in the black family which arent...healthy and as the relationship progresses he insults peter for EVERYTHUNG (his class, his E in jistrly of magic, his fair, his face and so on) and peter doesn't mind bc he knos regulus is weaker (physically) than him so he let's him "have his way" w him bc at the end of the day peter would still be on top and in full power and if he treats sirius like this he'd have 6 lost bones, 8 concussions, and a coffin in the ground
Ev they break up once regulus grows phy and grows further away from looking like sirius so peter dips and their break up conversation is like
Peter "im breaking up w u"
Regulus : "oh. ok "
And then regulus doesn't get out of bed except for classes for like 3 weeks bc he litr dated a 0/10 LOSER (his opinion) and still got dumped?!!?!
Nxt time they meet its a voldy meeting and regukus swears to himself he'll be a bttr death eat3r than pefer and is always eager to join like meetings and stuff (none of the otger death eaters really want him there tho)
