What makes a vagina loose?

My girlfriend and I of the last 2 years have had a great sex life. The last three months or so, her interest has seem to have wained off, and we went from doing it maybe 5+ times a week, to bout once in the last three weeks. occasionally we do play around with toys and such, but she seems more and more uninterested. and today, we happened to be fooling around, I noticed that when i stuck my fingers in her, she was extremely loose. the only times i've ever felt that is after lots of sex w/ her or her using one of our toys. she has no toys for herself, and have been wondering if she's been getting too close to her ex-boyfriend again. my question is, is there another explanation on why she would be loose like this? normally, she's extremely tight unless we've been doing a lot in the past day. and before today, i hadn't touched her in several days. thanx Tweet