Depends on your perspective I guess. They're on the couch making out at that time on certain nights and they're also in Mom's room doing even more. Presumably they would still be doing that whether you actually saw them or not. So IMO you're not really avoiding it, just sticking your head in the sand. It still happens either way.Yes, but it has no effect. It's not necessary to progress in any opportunity. You can decide not to do it and everything will play out exactly the same way. You can still kick Eric out, you can progress with Lisa, there will be no change.
So yes, it can be avoided.
If you're not home when someone robs your house, does that mean it didn't get robbed just because you didn't see it? Your stuff is still gone...