Not sure how she feels

I met a woman over the internet and we quickly became friends. I met her after about 6 months and we had sex...that was about 5 months ago. We see each other about once a month for lunch or whatever. So she texts me good morning on her work break and good night every night...we probably send an averages of 150 texts back and forth everyday. Over the last month her texts are a bit less enthusiastic and it has been harder to get her to meet. I guess my question is...if she seems distant is it just because it's hard to constantly text or is she texting a bunch of other guys?

Hi Mburger,

Consider answering my question, are you guys in a committed relationship?

If yes, you have full rights to worry about the present situation and/or whether she is texting a bunch of other guys ?
If no, then, you should be least bothered about her texting to other guys. Just because, you guys are good friends, talk with each other every night or had sex doesn't give you any authority to question about her personal life. What I mean to say is, even if she is texting other guys, she can do it and you should feel comfortable about it.

Wait for couple of days more. Don't make any judgments as of now. There is a finite possibility that she might be busy with some thing and hence she is not able to keep up the frequency of texts.
In anyways, you should talk to her. Text is always not a great choice. Call her or meet her in person, if possible and ask her directly whatever your doubts are. Its been 5 months since you guys met. Its time when you should consider meeting again, perhaps. Even on call, try to talk more about her and her life and ask her what's happening. She will only give you a clear picture.

Why are you only able to see each other once a month? If it's because of the distance then this is doomed - she's probably getting bored.