Ex/FWB starting to pull away

Long story short, dated my now ex from August till December non-exclusively. We were official for about a week and things just immediately didn’t feel right to me and we both agreed it would be best to break up. However, we both enjoyed the sex very much and did not want to give this up quite yet. We have been sleeping together about once per week. He continues to text me daily since we broke up in December. i don’t want him back, nor would I ever want him back given we are very incompatible, but I do notice his texts within the last week or so seem to be shorter, or that he takes longer to respond.

Normally, in most situations if this were someone I was still dating, I’d take my time responding as well. But I don’t want to have to find a new hook up buddy. It’s possible he’s now sleeping with someone else, as he has never appeared to withdraw like this before. Oddly enough, we slept together on valentine’s day and he had given me a card, chocolate, and lotion beforehand. So what the heck gives?