I work intimately in a team with 5 others. The nature of the work is often harrowing at times and we're encouraged to bond with & look out for one another. So far so good. I love the job & the kinship it's developed. We've all got to know one another warts-n-all. In the last few months I've realised one of my colleagues is attracted to me. I like him too. But he has a live-in gf. Their relationship has been on the rocks for ages & I expect they'll split before too long. Our group quite regularly meets in twos or threes out of hours to socialise or talk about the work if it's been especially difficult. The last time this happened though I had to draw a firm boundary for this chap. I like him a lot but I'm not about to become anyones bit on the side. All has been ok since until today. I've just had an invite to go out on a drive with him later in the week. I'm really not comfortable with this at all. I do not want to morph into 'the other woman'. At the same time, we have a brilliant working relationship and I don't want to spoil that. He needs to sort out his private life. I'm sure he does intend only an innocent day-trip but I bet his gf wouldn't be happy about it. How do I turn him down nicely & encourage him to sort his life out?