I agree that it's not too hard to conclude that Travis had sex with Jodi on June 4th considering the pictures we have seen from that day, together with the many times that he got pulled back into her web after seeming to realize that she was really bad news.
He had a lot of difficulty breaking away from her -- that's how relationships go with these types of personality disordered individuals. They are masterful at sucking their target back in.
I also believe that when Travis wrote the stern messages on May 26 calling her a sociopath and evil and the worst thing that ever happened to him, he very much meant what he said. And it seems that he stuck to it for a few days because there was very little communication between them from May 26 until June 2 when Jodi started her murder trip.
I do not believe Travis knew that Jodi was coming to Mesa prior to her early-morning arrival ...even Jodi has had a hard time saying that Travis knew she was coming. But once she arrived, it seems Jodi somehow talked her way in and got him to relax and feel comfortable letting his guard down. This is not hard to believe since Jodi obviously was able to persuade Travis numerous times to ignore the warning signs and just go with the flow.
Jodi could have proposed one final romp in the hay for old time's sake before she embarked on this new relationship with Ryan; or she could have just asked to sleep before getting back on the road, then seduced him, or Travis could have been completely ready and willing, ignoring his own gut instincts about her because he really did not think he was in any danger ...I don't think most guys in that situation would have thought they were going to become a victim of a brutal homicide a couple of hours after having sex with an ex-girlfriend.