Ever seen an abusive relationship? One of the first and strongest signs that things are going south is that the abuser will try to shut off any other options the abused might have. The abused will be forbidden from so much as spending time with members of the gender to which the abused is attracted. Abusers do this because they know that if the abused thinks that the abuser is the only romantic option available to them, they'll be far more likely to stay in the relationship. Unhealthy relationships thrive in isolation.
Abusers caught onto this principle, I noticed it because I've known my fair share of people in such relationships, and I realized that it's true in general. I looked at the sort of relationships my less romantically attractive friends were in. Liv and Ryan, two friends of mine, are both in situations where they really only have eachother as options. They both know it, and as such they don't try hard in their relationship. They don't bother trying to be better, kinder, or more engaged with one another because they know that as long as they remain better than nothing, they'll be able to keep the relationship going.
On the other hand, when you know that your partner is a catch, and you're lucky to have them, you tend to appreciate them more. When you know that you're valuable and have options, you're more likely to demand proper treatment from your partner. Intentionally isolating yourself or your partner has the potential to leave your relationship festering in complacency.
okay, i guess you got a good reasoning. but in a normal relationship, you shouldn't WANT to put anyone above your own partner, and if you do, i'm wondering what the hell you're doing in a relationship with this person in the first place
also most girls (and boys) have a [censored] self confidence so you can't really count on that either