I don't think that needing space is automatically code for needing space to have an affair or already having an affair. Admittedly, some people may use it as such, though.
My (MLC) H told me he needed time apart, but when we discussed requirements for this time period, he very readily agreed that he would not be seeing anyone else. He said himself that such behavior would cause irretrievable damage and he would not do it. I know that I'm not supposed to trust anything he says according to many folks here, but I choose to believe him on this point.
So.... just because you hear the words, try not to jump straight to conclusions. Maybe there really is an affair, but it's not a given. Some people just really are lost and need time to sort out the mess in their heads.
Maybe I'm naive, but I'd rather think the best until proven otherwise.
H: 44, Me: 45 Married: 20 y Together: 25 y no kids Walk away: 12/15 Asked for temp separation 12/25/15 PA confirmed 3/16 (apparently neither the first, nor the last PA he has had) H filed for D 5/16