For the most part, yes. There are some exceptions to it (e.g. Lena can still fuck Seymour even with ongoing trinity, and feel all conflicted about it afterwards) but many points where otherwise player is given a choice whether to have sex with someone automatically resolve to "nope, thanks". Trinity is a "pure romance" route extended to three people. Seymour being exception can be explained as his route being the "dark path" so to speak and a direct counter to the pure romance attitude.To be clear, does this mean that (at least since the three-way beach house update), once you're in the Trinity, no matter what else was selected in the game before, neither Ian or Lena can sleep with anyone outside the Trinity as of this update? (either greyed-out selection or option just not showing at all)?
(cue anakin/obiwan meme)