Hey guys, appreciate any advice you can give me.
I was in an LTR for nearly 5 years. Awesome girl, great future, wanted marriage, house, kids, the whole 9. I thought I was going to wind up marrying her. We broke up about 5 months ago because many issues were starting to pile up, mainly trust issues between us (I did cheat on her a long time ago, and then caught her messaging a couple ex-fbs behind my back) and that the passion died out of the relationship. She did initiate the break-up, but wanted to remain friends. Up until last month, I got frustrated at how bad I felt I was being treated by her (keep in mind we never had sex after we broke up). I told her that I didn't want to be friends anymore, for many reasons. I want you to either commit to me or I'm done. Needless to say she didn't commit and we went our separate ways.
Last week I was picking up my lunch at the shopping centre and she approached me while I was ordering. We chatted for about 5 minutes about what was going on in our lives and then I had to leave. Now, she just texted me this last night at 1AM.
"Thinking of you tonight...hope you're doing good

"
With everything that has happened, I wouldn't want a relationship SPAM (I am dating other girls), but I would be open to a FB/FWB type of situation. I don't think she's looking for validation given that she approached me and initiated conversation in the shopping centre? How do I respond? Thanks for any advice.
PS. Was thinking of saying "Hey, I am doing great, how are you?"