Of course, it's harder for them to be monogomous. Even if they aren't cruising for sexual encounters, they just have way more opportunity. I'm a woman married to a man. (duh). All of my girlfriends are - well - girls. They aren't all possible sexual partners.
I know a very nice lesbian couple who have been together for several years, but they are highly possessive of one another and only hang out with each other's families. They don't trust the other to have goof female friendshps - not other lesbians, anyway!
This would suggest sexual identity problems at both extremems of the spectrum, IMHO.