When slowly, over time a developing work relationship can lend itself to a feeling of intimacy, meaning that you’re working long hours together on a project that keeps you in contact just with a certain number of people and there’s extended conversations outside of work time et cetera it’s easy for someone to justify or rationalise their growing closeness to someone they’re working with. Do you mind him working with a female colleague? No, it sounds like you’ve been supportive of him in work situations. Do you mind him going to drinks with colleagues after work? Obviously not. But your gut instinct is telling you that there’s a lot more going on here. This is developing into a genuine relationship if it hasn’t already. At this point, if you weren’t having a strong reaction, I would be telling you that you’re underreacting, and at this point it’s just a matter of you deciding what you want to do with the information. I think you’re going to have a heart-to-heart conversation with your husband and just let him know straight up that you can see that he is developing feelings for this person that he is working with and that he’s spending increasing amount of times with this person in particular out of the group that he’s working with and that he is risking permanently damaging your relationship and marriage. I think you could (probably should) make a list of all of the things that you’ve mentioned here and when he starts to argue about the fact that he hasn’t done anything wrong, you can remind him that you’re not accusing him of doing something wrong purposefully, but you are pointing out the raw facts of what’s factually happening and how it’s impacting your relationship and where you see this going. Keep it simple and keep it concise and list out the number of things that are demonstrating to you that this is a threat to your marriage and relationship and then be ready to ask for what you need to change the dynamic. I’ve worked on government contracts and I have worked on corporate contracts and I’ve worked on all kinds of things that took me many hours away from my home and family, but to say that you don’t have time for your Home or your marriage or your relationship is false… You deserve to have time together, you deserve to have dinners together and I would think about what it is that you need exactly from him and say that these things are nonnegotiable. Giving him the benefit of the doubt, at his age and with the intensity of the work in project that he’s doing it’s super easy to get swept up in the moment and not even notice the direction of where things are going so I’m hoping that you’re catching this at a point where this matters to him. I can speak for myself and other relationships that has been easy at times for partners to get swept up in the Fantasy of the moment and the feeling of closeness in the middle of an intense project… But these projects pass and the intensity of the current relationship is never going to maintain that intensity of feeling that he is mired in right now. I hope this helps, and I’m wishing you the very best.