I have suspected that there is a chemistry between Alex and Kate since week 2. She started off by openly admitting to everyone that she fancied Alex. As soon as he admitted that he too fancied her, two or three days later she went off him and started flirting with Spenser, claiming that she was not attracted to him anymore because he is a perfectionist.
If l was in his position l too would be confused and a bit jealous. She did not explain why she had changed her mind about him. One minute she was all over him flirting and then the next minute she was flirting with Spenser.
It is no surprise then that when Sandy came out with his lion analogy that he jumped all over it and agreed that Kate was the house whore. That was the only way he could explain her behaviour.
All the petty arguements between them since has been fuelled l believe by jealousy. Kate's relationship with Spenser made Alex jealous and Adele relationship with Alex made Kate jealous - (several incidences like, Kate told Adele a dream she had in which she burnt Adele's car and wrote bitch all over it. When she saw Alex kissing Adele that same evening she got inbewteen them in the bed and started kissing Alex and Adele)
Now Adele and Spenser are out of the way they were bonding in a physical way, very quickly. But with Jonny, PJ and Tim making them feel self conscious (asking questions about follow the van game) Kate/Alex are worried that they may be percieved as slappers outside of the house. As a result they are now distancing themselves from one another.
I agree with some of the previous posts. I don't think they will get together after this because there has been too many distractions and obsticles in their way. They are, l believe in denial of their true feelings for fear of being percieved in a negative way - too flirtatous. A fear which they have both voiced openly with other housemates.